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 $223.66   7.762%   $241.0205   $241.02   $241.00   $241.00  
  Purchase #2 $241.54   5.528%   $254.8923   $254.89   $254.90   $254.90  
  Purchase #3 $123.55   13.311%   $139.9957   $140.00   $140.00   $140.00  
  Purchase #4 $91.87   8.360%   $99.5503   $99.55   $99.55   $99.60  
  Purchase #5 $189.82   7.719%   $204.4722   $204.47   $204.45   $204.50  
  Purchase #6 $160.42   8.351%   $173.8167   $173.82   $173.80   $173.80  
  Purchase #7 $84.37   12.103%   $94.5813   $94.58   $94.60   $94.60  
  7 purchase totals = $1,115.23       $1,208.3290   $1,208.33   $1,208.30   $1,208.40