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 $238.25   12.623%   $268.3243   $268.32   $268.30   $268.30  
  Purchase #2 $154.87   12.443%   $174.1405   $174.14   $174.15   $174.10  
  Purchase #3 $245.99   3.597%   $254.8383   $254.84   $254.85   $254.80  
  Purchase #4 $63.65   12.708%   $71.7386   $71.74   $71.75   $71.70  
  Purchase #5 $118.31   13.140%   $133.8559   $133.86   $133.85   $133.90  
  Purchase #6 $50.68   5.299%   $53.3655   $53.37   $53.35   $53.40  
  Purchase #7 $10.29   5.585%   $10.8647   $10.86   $10.85   $10.90  
  7 purchase totals = $882.04       $967.1278   $967.13   $967.10   $967.10