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 $110.51   13.719%   $125.6709   $125.67   $125.65   $125.70  
  Purchase #2 $39.46   5.349%   $41.5707   $41.57   $41.55   $41.60  
  Purchase #3 $102.62   8.130%   $110.963   $110.96   $110.95   $111.00  
  Purchase #4 $25.70   4.608%   $26.8843   $26.88   $26.90   $26.90  
  Purchase #5 $111.70   3.574%   $115.6922   $115.69   $115.70   $115.70  
  Purchase #6 $62.30   13.192%   $70.5186   $70.52   $70.50   $70.50  
  Purchase #7 $156.89   13.526%   $178.1109   $178.11   $178.10   $178.10  
  7 purchase totals = $609.18       $669.4106   $669.40   $669.35   $669.50