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 $244.86   12.317%   $275.0194   $275.02   $275.00   $275.00  
  Purchase #2 $84.94   8.783%   $92.4003   $92.40   $92.40   $92.40  
  Purchase #3 $111.62   7.297%   $119.7649   $119.76   $119.75   $119.80  
  Purchase #4 $140.81   4.224%   $146.7578   $146.76   $146.75   $146.80  
  Purchase #5 $163.79   6.711%   $174.7819   $174.78   $174.80   $174.80  
  Purchase #6 $46.66   11.277%   $51.9218   $51.92   $51.90   $51.90  
  Purchase #7 $186.99   8.745%   $203.3423   $203.34   $203.35   $203.30  
  7 purchase totals = $979.67       $1,063.9884   $1,063.98   $1,063.95   $1,064.00