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 $192.70   8.785%   $209.6287   $209.63   $209.65   $209.60  
  Purchase #2 $59.98   11.798%   $67.0564   $67.06   $67.05   $67.10  
  Purchase #3 $85.84   13.375%   $97.3211   $97.32   $97.30   $97.30  
  Purchase #4 $91.41   5.713%   $96.6323   $96.63   $96.65   $96.60  
  Purchase #5 $60.75   12.782%   $68.5151   $68.52   $68.50   $68.50  
  Purchase #6 $188.38   13.140%   $213.1331   $213.13   $213.15   $213.10  
  Purchase #7 $229.54   5.804%   $242.8625   $242.86   $242.85   $242.90  
  7 purchase totals = $908.60       $995.1492   $995.15   $995.15   $995.10