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 $25.52   3.203%   $26.3374   $26.34   $26.35   $26.30  
  Purchase #2 $245.85   9.680%   $269.6483   $269.65   $269.65   $269.60  
  Purchase #3 $169.77   10.487%   $187.5738   $187.57   $187.55   $187.60  
  Purchase #4 $99.34   3.820%   $103.1348   $103.13   $103.15   $103.10  
  Purchase #5 $71.92   10.570%   $79.5219   $79.52   $79.50   $79.50  
  Purchase #6 $241.63   9.199%   $263.8575   $263.86   $263.85   $263.90  
  Purchase #7 $26.77   6.444%   $28.4951   $28.50   $28.50   $28.50  
  7 purchase totals = $880.80       $958.5688   $958.57   $958.55   $958.50