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 $88.88   10.216%   $97.96   $97.96   $97.95   $98.00  
  Purchase #2 $169.35   6.399%   $180.1867   $180.19   $180.20   $180.20  
  Purchase #3 $50.96   7.582%   $54.8238   $54.82   $54.80   $54.80  
  Purchase #4 $36.97   11.868%   $41.3576   $41.36   $41.35   $41.40  
  Purchase #5 $137.93   7.416%   $148.1589   $148.16   $148.15   $148.20  
  Purchase #6 $140.94   9.263%   $153.9953   $154.00   $154.00   $154.00  
  Purchase #7 $59.97   8.435%   $65.0285   $65.03   $65.05   $65.00  
  7 purchase totals = $685.00       $741.5108   $741.52   $741.50   $741.60