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 $62.64   6.730%   $66.8557   $66.86   $66.85   $66.90  
  Purchase #2 $29.61   12.177%   $33.2156   $33.22   $33.20   $33.20  
  Purchase #3 $175.36   5.377%   $184.7891   $184.79   $184.80   $184.80  
  Purchase #4 $132.27   13.263%   $149.813   $149.81   $149.80   $149.80  
  Purchase #5 $5.44   9.391%   $5.9509   $5.95   $5.95   $6.00  
  Purchase #6 $169.60   6.255%   $180.2085   $180.21   $180.20   $180.20  
  Purchase #7 $100.54   12.475%   $113.0824   $113.08   $113.10   $113.10  
  7 purchase totals = $675.46       $733.9152   $733.92   $733.90   $734.00