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 $53.53   10.516%   $59.1592   $59.16   $59.15   $59.20  
  Purchase #2 $91.38   4.759%   $95.7288   $95.73   $95.75   $95.70  
  Purchase #3 $204.79   10.352%   $225.9899   $225.99   $226.00   $226.00  
  Purchase #4 $114.30   6.334%   $121.5398   $121.54   $121.55   $121.50  
  Purchase #5 $96.56   5.102%   $101.4865   $101.49   $101.50   $101.50  
  Purchase #6 $246.59   13.827%   $280.686   $280.69   $280.70   $280.70  
  Purchase #7 $48.99   11.858%   $54.7992   $54.80   $54.80   $54.80  
  7 purchase totals = $856.14       $939.3894   $939.40   $939.45   $939.40