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 $59.94   7.262%   $64.2928   $64.29   $64.30   $64.30  
  Purchase #2 $191.80   7.404%   $206.0009   $206.00   $206.00   $206.00  
  Purchase #3 $88.44   5.571%   $93.367   $93.37   $93.35   $93.40  
  Purchase #4 $79.63   11.490%   $88.7795   $88.78   $88.80   $88.80  
  Purchase #5 $25.94   11.634%   $28.9579   $28.96   $28.95   $29.00  
  Purchase #6 $157.42   3.123%   $162.3362   $162.34   $162.35   $162.30  
  Purchase #7 $180.52   11.295%   $200.9097   $200.91   $200.90   $200.90  
  7 purchase totals = $783.69       $844.6440   $844.65   $844.65   $844.70