Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.74   11.262%   $197.7571   $197.76   $197.75   $197.80  
  Purchase #2 $152.58   13.387%   $173.0059   $173.01   $173.00   $173.00  
  Purchase #3 $210.72   8.283%   $228.1739   $228.17   $228.15   $228.20  
  Purchase #4 $118.86   6.176%   $126.2008   $126.20   $126.20   $126.20  
  Purchase #5 $185.69   12.638%   $209.1575   $209.16   $209.15   $209.20  
  Purchase #6 $212.32   10.115%   $233.7962   $233.80   $233.80   $233.80  
  Purchase #7 $175.74   11.191%   $195.4071   $195.41   $195.40   $195.40  
  7 purchase totals = $1,233.65       $1,363.4985   $1,363.51   $1,363.45   $1,363.60