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 $82.28   11.706%   $91.9117   $91.91   $91.90   $91.90  
  Purchase #2 $212.86   6.628%   $226.9684   $226.97   $226.95   $227.00  
  Purchase #3 $192.37   7.434%   $206.6708   $206.67   $206.65   $206.70  
  Purchase #4 $85.38   11.355%   $95.0749   $95.07   $95.05   $95.10  
  Purchase #5 $235.69   12.292%   $264.661   $264.66   $264.65   $264.70  
  Purchase #6 $185.69   10.720%   $205.596   $205.60   $205.60   $205.60  
  Purchase #7 $219.86   9.405%   $240.5378   $240.54   $240.55   $240.50  
  7 purchase totals = $1,214.13       $1,331.4206   $1,331.42   $1,331.35   $1,331.50