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 $56.98   12.647%   $64.1863   $64.19   $64.20   $64.20  
  Purchase #2 $245.83   5.813%   $260.1201   $260.12   $260.10   $260.10  
  Purchase #3 $24.38   13.806%   $27.7459   $27.75   $27.75   $27.70  
  Purchase #4 $105.65   10.842%   $117.1046   $117.10   $117.10   $117.10  
  Purchase #5 $91.41   4.170%   $95.2218   $95.22   $95.20   $95.20  
  Purchase #6 $134.95   8.487%   $146.4032   $146.40   $146.40   $146.40  
  Purchase #7 $147.95   11.192%   $164.5086   $164.51   $164.50   $164.50  
  7 purchase totals = $807.15       $875.2905   $875.29   $875.25   $875.20