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 $44.71   13.213%   $50.6175   $50.62   $50.60   $50.60  
  Purchase #2 $31.38   13.413%   $35.589   $35.59   $35.60   $35.60  
  Purchase #3 $71.39   3.218%   $73.6873   $73.69   $73.70   $73.70  
  Purchase #4 $161.80   5.160%   $170.1489   $170.15   $170.15   $170.10  
  Purchase #5 $61.26   4.847%   $64.2293   $64.23   $64.25   $64.20  
  Purchase #6 $165.37   13.297%   $187.3592   $187.36   $187.35   $187.40  
  Purchase #7 $110.33   11.220%   $122.709   $122.71   $122.70   $122.70  
  7 purchase totals = $646.24       $704.3402   $704.35   $704.35   $704.30