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 $49.53   10.244%   $54.6039   $54.60   $54.60   $54.60  
  Purchase #2 $162.86   12.309%   $182.9064   $182.91   $182.90   $182.90  
  Purchase #3 $71.88   10.156%   $79.1801   $79.18   $79.20   $79.20  
  Purchase #4 $176.26   3.358%   $182.1788   $182.18   $182.20   $182.20  
  Purchase #5 $203.32   12.105%   $227.9319   $227.93   $227.95   $227.90  
  Purchase #6 $247.58   9.306%   $270.6198   $270.62   $270.60   $270.60  
  Purchase #7 $31.45   12.347%   $35.3331   $35.33   $35.35   $35.30  
  7 purchase totals = $942.88       $1,032.7540   $1,032.75   $1,032.80   $1,032.70