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 $59.60   13.705%   $67.7682   $67.77   $67.75   $67.80  
  Purchase #2 $236.41   4.114%   $246.1359   $246.14   $246.15   $246.10  
  Purchase #3 $203.36   10.814%   $225.3514   $225.35   $225.35   $225.40  
  Purchase #4 $198.63   10.203%   $218.8962   $218.90   $218.90   $218.90  
  Purchase #5 $23.30   9.192%   $25.4417   $25.44   $25.45   $25.40  
  Purchase #6 $55.26   10.673%   $61.1579   $61.16   $61.15   $61.20  
  Purchase #7 $121.46   8.314%   $131.5582   $131.56   $131.55   $131.60  
  7 purchase totals = $898.02       $976.3095   $976.32   $976.30   $976.40