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 $34.51   9.186%   $37.6801   $37.68   $37.70   $37.70  
  Purchase #2 $232.35   12.452%   $261.2822   $261.28   $261.30   $261.30  
  Purchase #3 $52.56   4.228%   $54.7822   $54.78   $54.80   $54.80  
  Purchase #4 $72.54   3.541%   $75.1086   $75.11   $75.10   $75.10  
  Purchase #5 $96.73   12.106%   $108.4401   $108.44   $108.45   $108.40  
  Purchase #6 $42.41   4.238%   $44.2073   $44.21   $44.20   $44.20  
  Purchase #7 $233.56   11.526%   $260.4801   $260.48   $260.50   $260.50  
  7 purchase totals = $764.66       $841.9806   $841.98   $842.05   $842.00