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 $181.26   11.866%   $202.7683   $202.77   $202.75   $202.80  
  Purchase #2 $41.35   8.162%   $44.725   $44.73   $44.75   $44.70  
  Purchase #3 $201.29   5.715%   $212.7937   $212.79   $212.80   $212.80  
  Purchase #4 $82.27   4.787%   $86.2083   $86.21   $86.20   $86.20  
  Purchase #5 $65.70   10.403%   $72.5348   $72.53   $72.55   $72.50  
  Purchase #6 $102.43   9.416%   $112.0748   $112.07   $112.05   $112.10  
  Purchase #7 $14.92   11.355%   $16.6142   $16.61   $16.60   $16.60  
  7 purchase totals = $689.22       $747.7191   $747.71   $747.70   $747.70