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 $173.48   10.413%   $191.5445   $191.54   $191.55   $191.50  
  Purchase #2 $24.58   8.621%   $26.699   $26.70   $26.70   $26.70  
  Purchase #3 $93.78   3.553%   $97.112   $97.11   $97.10   $97.10  
  Purchase #4 $190.69   10.654%   $211.0061   $211.01   $211.00   $211.00  
  Purchase #5 $59.42   9.334%   $64.9663   $64.97   $64.95   $65.00  
  Purchase #6 $5.88   6.536%   $6.2643   $6.26   $6.25   $6.30  
  Purchase #7 $158.26   6.428%   $168.433   $168.43   $168.45   $168.40  
  7 purchase totals = $706.09       $766.0252   $766.02   $766.00   $766.00