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 $232.73   7.836%   $250.9667   $250.97   $250.95   $251.00  
  Purchase #2 $176.58   8.421%   $191.4498   $191.45   $191.45   $191.40  
  Purchase #3 $78.90   7.466%   $84.7907   $84.79   $84.80   $84.80  
  Purchase #4 $242.32   9.529%   $265.4107   $265.41   $265.40   $265.40  
  Purchase #5 $90.68   4.475%   $94.7379   $94.74   $94.75   $94.70  
  Purchase #6 $126.82   8.567%   $137.6847   $137.68   $137.70   $137.70  
  Purchase #7 $183.73   7.744%   $197.9581   $197.96   $197.95   $198.00  
  7 purchase totals = $1,131.76       $1,222.9986   $1,223.00   $1,223.00   $1,223.00