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 $61.38   11.417%   $68.3878   $68.39   $68.40   $68.40  
  Purchase #2 $224.89   13.430%   $255.0927   $255.09   $255.10   $255.10  
  Purchase #3 $208.26   13.759%   $236.9145   $236.91   $236.90   $236.90  
  Purchase #4 $216.60   4.476%   $226.295   $226.30   $226.30   $226.30  
  Purchase #5 $16.30   13.541%   $18.5072   $18.51   $18.50   $18.50  
  Purchase #6 $43.27   10.237%   $47.6995   $47.70   $47.70   $47.70  
  Purchase #7 $216.75   9.552%   $237.454   $237.45   $237.45   $237.50  
  7 purchase totals = $987.45       $1,090.3507   $1,090.35   $1,090.35   $1,090.40