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 $244.56   12.651%   $275.4993   $275.50   $275.50   $275.50  
  Purchase #2 $196.65   4.821%   $206.1305   $206.13   $206.15   $206.10  
  Purchase #3 $112.75   11.220%   $125.4006   $125.40   $125.40   $125.40  
  Purchase #4 $55.61   7.184%   $59.605   $59.61   $59.60   $59.60  
  Purchase #5 $186.97   6.570%   $199.2539   $199.25   $199.25   $199.30  
  Purchase #6 $199.25   6.862%   $212.9225   $212.92   $212.90   $212.90  
  Purchase #7 $75.70   9.293%   $82.7348   $82.73   $82.75   $82.70  
  7 purchase totals = $1,071.49       $1,161.5466   $1,161.54   $1,161.55   $1,161.50