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 $58.98   3.873%   $61.2643   $61.26   $61.25   $61.30  
  Purchase #2 $89.37   8.797%   $97.2319   $97.23   $97.25   $97.20  
  Purchase #3 $15.45   9.137%   $16.8617   $16.86   $16.85   $16.90  
  Purchase #4 $107.96   13.600%   $122.6426   $122.64   $122.65   $122.60  
  Purchase #5 $204.74   10.662%   $226.5694   $226.57   $226.55   $226.60  
  Purchase #6 $182.82   11.459%   $203.7693   $203.77   $203.75   $203.80  
  Purchase #7 $90.65   10.343%   $100.0259   $100.03   $100.05   $100.00  
  7 purchase totals = $749.97       $828.3651   $828.36   $828.35   $828.40