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 $249.77   5.210%   $262.783   $262.78   $262.80   $262.80  
  Purchase #2 $135.77   3.856%   $141.0053   $141.01   $141.00   $141.00  
  Purchase #3 $135.94   9.509%   $148.8665   $148.87   $148.85   $148.90  
  Purchase #4 $121.97   3.275%   $125.9645   $125.96   $125.95   $126.00  
  Purchase #5 $32.46   6.642%   $34.616   $34.62   $34.60   $34.60  
  Purchase #6 $39.75   10.489%   $43.9194   $43.92   $43.90   $43.90  
  Purchase #7 $22.75   13.466%   $25.8135   $25.81   $25.80   $25.80  
  7 purchase totals = $738.41       $782.9682   $782.97   $782.90   $783.00