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 $84.33   13.407%   $95.6361   $95.64   $95.65   $95.60  
  Purchase #2 $73.66   3.399%   $76.1637   $76.16   $76.15   $76.20  
  Purchase #3 $110.37   4.293%   $115.1082   $115.11   $115.10   $115.10  
  Purchase #4 $213.39   13.648%   $242.5135   $242.51   $242.50   $242.50  
  Purchase #5 $74.67   7.561%   $80.3158   $80.32   $80.30   $80.30  
  Purchase #6 $193.40   5.201%   $203.4587   $203.46   $203.45   $203.50  
  Purchase #7 $25.32   8.685%   $27.519   $27.52   $27.50   $27.50  
  7 purchase totals = $775.14       $840.7150   $840.72   $840.65   $840.70