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 $208.28   13.245%   $235.8667   $235.87   $235.85   $235.90  
  Purchase #2 $155.50   13.409%   $176.351   $176.35   $176.35   $176.40  
  Purchase #3 $84.83   7.199%   $90.9369   $90.94   $90.95   $90.90  
  Purchase #4 $27.51   7.375%   $29.5389   $29.54   $29.55   $29.50  
  Purchase #5 $200.25   10.203%   $220.6815   $220.68   $220.70   $220.70  
  Purchase #6 $83.67   11.399%   $93.2075   $93.21   $93.20   $93.20  
  Purchase #7 $221.73   13.161%   $250.9119   $250.91   $250.90   $250.90  
  7 purchase totals = $981.77       $1,097.4944   $1,097.50   $1,097.50   $1,097.50