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 $27.43   4.378%   $28.6309   $28.63   $28.65   $28.60  
  Purchase #2 $89.43   4.302%   $93.2773   $93.28   $93.30   $93.30  
  Purchase #3 $56.58   11.370%   $63.0131   $63.01   $63.00   $63.00  
  Purchase #4 $48.34   9.243%   $52.8081   $52.81   $52.80   $52.80  
  Purchase #5 $48.52   12.147%   $54.4137   $54.41   $54.40   $54.40  
  Purchase #6 $194.60   6.321%   $206.9007   $206.90   $206.90   $206.90  
  Purchase #7 $243.39   5.430%   $256.6061   $256.61   $256.60   $256.60  
  7 purchase totals = $708.29       $755.6499   $755.65   $755.65   $755.60