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 $66.46   4.436%   $69.4082   $69.41   $69.40   $69.40  
  Purchase #2 $24.29   7.137%   $26.0236   $26.02   $26.00   $26.00  
  Purchase #3 $110.93   5.403%   $116.9235   $116.92   $116.90   $116.90  
  Purchase #4 $119.61   4.846%   $125.4063   $125.41   $125.40   $125.40  
  Purchase #5 $185.59   11.562%   $207.0479   $207.05   $207.05   $207.00  
  Purchase #6 $60.94   3.165%   $62.8688   $62.87   $62.85   $62.90  
  Purchase #7 $115.91   4.255%   $120.842   $120.84   $120.85   $120.80  
  7 purchase totals = $683.73       $728.5203   $728.52   $728.45   $728.40