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 $64.75   5.188%   $68.1092   $68.11   $68.10   $68.10  
  Purchase #2 $83.57   13.627%   $94.9581   $94.96   $94.95   $95.00  
  Purchase #3 $207.83   6.628%   $221.605   $221.61   $221.60   $221.60  
  Purchase #4 $227.28   11.677%   $253.8195   $253.82   $253.80   $253.80  
  Purchase #5 $97.86   5.687%   $103.4253   $103.43   $103.45   $103.40  
  Purchase #6 $61.37   8.127%   $66.3575   $66.36   $66.35   $66.40  
  Purchase #7 $56.35   4.739%   $59.0204   $59.02   $59.00   $59.00  
  7 purchase totals = $799.01       $867.2950   $867.31   $867.25   $867.30