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 $181.98   11.527%   $202.9568   $202.96   $202.95   $203.00  
  Purchase #2 $45.59   3.788%   $47.3169   $47.32   $47.30   $47.30  
  Purchase #3 $201.52   9.780%   $221.2287   $221.23   $221.25   $221.20  
  Purchase #4 $87.76   7.416%   $94.2683   $94.27   $94.25   $94.30  
  Purchase #5 $162.39   6.816%   $173.4585   $173.46   $173.45   $173.50  
  Purchase #6 $160.86   7.827%   $173.4505   $173.45   $173.45   $173.50  
  Purchase #7 $71.77   11.389%   $79.9439   $79.94   $79.95   $79.90  
  7 purchase totals = $911.87       $992.6236   $992.63   $992.60   $992.70