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 $228.33   13.148%   $258.3508   $258.35   $258.35   $258.40  
  Purchase #2 $206.66   13.855%   $235.2927   $235.29   $235.30   $235.30  
  Purchase #3 $25.76   3.699%   $26.7129   $26.71   $26.70   $26.70  
  Purchase #4 $35.53   13.380%   $40.2839   $40.28   $40.30   $40.30  
  Purchase #5 $187.65   6.516%   $199.8773   $199.88   $199.90   $199.90  
  Purchase #6 $192.82   11.569%   $215.1273   $215.13   $215.15   $215.10  
  Purchase #7 $135.85   4.167%   $141.5109   $141.51   $141.50   $141.50  
  7 purchase totals = $1,012.60       $1,117.1558   $1,117.15   $1,117.20   $1,117.20