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 $250.34   4.662%   $262.0109   $262.01   $262.00   $262.00  
  Purchase #2 $31.79   10.454%   $35.1133   $35.11   $35.10   $35.10  
  Purchase #3 $132.45   7.662%   $142.5983   $142.60   $142.60   $142.60  
  Purchase #4 $124.59   12.378%   $140.0118   $140.01   $140.00   $140.00  
  Purchase #5 $21.58   8.644%   $23.4454   $23.45   $23.45   $23.40  
  Purchase #6 $139.49   4.379%   $145.5983   $145.60   $145.60   $145.60  
  Purchase #7 $41.90   6.808%   $44.7526   $44.75   $44.75   $44.80  
  7 purchase totals = $742.14       $793.5306   $793.53   $793.50   $793.50