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 $58.73   13.280%   $66.5293   $66.53   $66.55   $66.50  
  Purchase #2 $124.82   8.177%   $135.0265   $135.03   $135.05   $135.00  
  Purchase #3 $40.32   10.160%   $44.4165   $44.42   $44.40   $44.40  
  Purchase #4 $158.97   13.766%   $180.8538   $180.85   $180.85   $180.90  
  Purchase #5 $69.66   6.158%   $73.9497   $73.95   $73.95   $73.90  
  Purchase #6 $96.41   12.201%   $108.173   $108.17   $108.15   $108.20  
  Purchase #7 $165.99   3.407%   $171.6453   $171.65   $171.65   $171.60  
  7 purchase totals = $714.90       $780.5941   $780.60   $780.60   $780.50