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 $87.72   8.273%   $94.9771   $94.98   $95.00   $95.00  
  Purchase #2 $48.74   4.364%   $50.867   $50.87   $50.85   $50.90  
  Purchase #3 $124.81   8.559%   $135.4925   $135.49   $135.50   $135.50  
  Purchase #4 $53.29   13.413%   $60.4378   $60.44   $60.45   $60.40  
  Purchase #5 $97.96   5.233%   $103.0862   $103.09   $103.10   $103.10  
  Purchase #6 $55.43   12.431%   $62.3205   $62.32   $62.30   $62.30  
  Purchase #7 $107.68   8.678%   $117.0245   $117.02   $117.00   $117.00  
  7 purchase totals = $575.63       $624.2056   $624.21   $624.20   $624.20