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 $59.29   12.562%   $66.738   $66.74   $66.75   $66.70  
  Purchase #2 $50.69   6.614%   $54.0426   $54.04   $54.05   $54.00  
  Purchase #3 $17.70   6.786%   $18.9011   $18.90   $18.90   $18.90  
  Purchase #4 $201.82   5.519%   $212.9584   $212.96   $212.95   $213.00  
  Purchase #5 $177.83   5.602%   $187.792   $187.79   $187.80   $187.80  
  Purchase #6 $170.76   4.181%   $177.8995   $177.90   $177.90   $177.90  
  Purchase #7 $28.47   7.120%   $30.4971   $30.50   $30.50   $30.50  
  7 purchase totals = $706.56       $748.8287   $748.83   $748.85   $748.80