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 $61.39   7.469%   $65.9752   $65.98   $66.00   $66.00  
  Purchase #2 $86.64   11.244%   $96.3818   $96.38   $96.40   $96.40  
  Purchase #3 $144.42   8.251%   $156.3361   $156.34   $156.35   $156.30  
  Purchase #4 $211.63   4.350%   $220.8359   $220.84   $220.85   $220.80  
  Purchase #5 $134.94   11.839%   $150.9155   $150.92   $150.90   $150.90  
  Purchase #6 $35.55   3.355%   $36.7427   $36.74   $36.75   $36.70  
  Purchase #7 $204.30   4.566%   $213.6283   $213.63   $213.65   $213.60  
  7 purchase totals = $878.87       $940.8155   $940.83   $940.90   $940.70