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 $233.70   3.226%   $241.2392   $241.24   $241.25   $241.20  
  Purchase #2 $163.47   13.659%   $185.7984   $185.80   $185.80   $185.80  
  Purchase #3 $47.72   9.858%   $52.4242   $52.42   $52.40   $52.40  
  Purchase #4 $68.38   10.668%   $75.6748   $75.67   $75.65   $75.70  
  Purchase #5 $97.80   12.614%   $110.1365   $110.14   $110.15   $110.10  
  Purchase #6 $231.64   6.205%   $246.0133   $246.01   $246.00   $246.00  
  Purchase #7 $17.60   12.152%   $19.7388   $19.74   $19.75   $19.70  
  7 purchase totals = $860.31       $931.0252   $931.02   $931.00   $930.90