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 $101.87   8.586%   $110.6166   $110.62   $110.60   $110.60  
  Purchase #2 $64.53   5.826%   $68.2895   $68.29   $68.30   $68.30  
  Purchase #3 $172.46   6.529%   $183.7199   $183.72   $183.70   $183.70  
  Purchase #4 $23.73   11.302%   $26.412   $26.41   $26.40   $26.40  
  Purchase #5 $117.79   11.389%   $131.2051   $131.21   $131.20   $131.20  
  Purchase #6 $207.27   13.329%   $234.897   $234.90   $234.90   $234.90  
  Purchase #7 $49.42   8.501%   $53.6212   $53.62   $53.60   $53.60  
  7 purchase totals = $737.07       $808.7613   $808.77   $808.70   $808.70