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 $71.55   5.650%   $75.5926   $75.59   $75.60   $75.60  
  Purchase #2 $233.83   12.872%   $263.9286   $263.93   $263.95   $263.90  
  Purchase #3 $56.73   13.219%   $64.2291   $64.23   $64.25   $64.20  
  Purchase #4 $100.44   11.416%   $111.9062   $111.91   $111.90   $111.90  
  Purchase #5 $132.92   12.640%   $149.7211   $149.72   $149.70   $149.70  
  Purchase #6 $97.29   10.841%   $107.8372   $107.84   $107.85   $107.80  
  Purchase #7 $144.79   13.683%   $164.6016   $164.60   $164.60   $164.60  
  7 purchase totals = $837.55       $937.8164   $937.82   $937.85   $937.70