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 $232.66   12.410%   $261.5331   $261.53   $261.55   $261.50  
  Purchase #2 $186.90   12.563%   $210.3802   $210.38   $210.40   $210.40  
  Purchase #3 $105.29   7.391%   $113.072   $113.07   $113.05   $113.10  
  Purchase #4 $70.85   6.772%   $75.648   $75.65   $75.65   $75.60  
  Purchase #5 $19.46   9.668%   $21.3414   $21.34   $21.35   $21.30  
  Purchase #6 $130.75   9.461%   $143.1203   $143.12   $143.10   $143.10  
  Purchase #7 $205.86   8.202%   $222.7446   $222.74   $222.75   $222.70  
  7 purchase totals = $951.77       $1,047.8396   $1,047.83   $1,047.85   $1,047.70