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 $146.68   8.328%   $158.8955   $158.90   $158.90   $158.90  
  Purchase #2 $14.69   10.365%   $16.2126   $16.21   $16.20   $16.20  
  Purchase #3 $165.58   13.413%   $187.7892   $187.79   $187.80   $187.80  
  Purchase #4 $199.33   8.791%   $216.8531   $216.85   $216.85   $216.90  
  Purchase #5 $44.79   13.715%   $50.9329   $50.93   $50.95   $50.90  
  Purchase #6 $245.53   7.477%   $263.8883   $263.89   $263.90   $263.90  
  Purchase #7 $61.62   4.446%   $64.3596   $64.36   $64.35   $64.40  
  7 purchase totals = $878.22       $958.9312   $958.93   $958.95   $959.00