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 $245.87   12.201%   $275.8686   $275.87   $275.85   $275.90  
  Purchase #2 $234.71   5.136%   $246.7647   $246.76   $246.75   $246.80  
  Purchase #3 $32.53   6.509%   $34.6474   $34.65   $34.65   $34.60  
  Purchase #4 $55.70   7.673%   $59.9739   $59.97   $59.95   $60.00  
  Purchase #5 $197.59   4.794%   $207.0625   $207.06   $207.05   $207.10  
  Purchase #6 $165.74   6.619%   $176.7103   $176.71   $176.70   $176.70  
  Purchase #7 $121.47   3.472%   $125.6874   $125.69   $125.70   $125.70  
  7 purchase totals = $1,053.61       $1,126.7148   $1,126.71   $1,126.65   $1,126.80