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 $30.59   6.359%   $32.5352   $32.54   $32.55   $32.50  
  Purchase #2 $247.26   8.197%   $267.5279   $267.53   $267.55   $267.50  
  Purchase #3 $128.91   7.197%   $138.1877   $138.19   $138.20   $138.20  
  Purchase #4 $219.46   4.481%   $229.294   $229.29   $229.30   $229.30  
  Purchase #5 $38.61   10.662%   $42.7266   $42.73   $42.75   $42.70  
  Purchase #6 $150.50   5.594%   $158.919   $158.92   $158.90   $158.90  
  Purchase #7 $153.59   7.382%   $164.928   $164.93   $164.95   $164.90  
  7 purchase totals = $968.92       $1,034.1184   $1,034.13   $1,034.20   $1,034.00