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 $236.58   5.289%   $249.0927   $249.09   $249.10   $249.10  
  Purchase #2 $195.56   10.440%   $215.9765   $215.98   $216.00   $216.00  
  Purchase #3 $197.98   8.402%   $214.6143   $214.61   $214.60   $214.60  
  Purchase #4 $10.73   6.567%   $11.4346   $11.43   $11.45   $11.40  
  Purchase #5 $173.86   6.140%   $184.535   $184.54   $184.55   $184.50  
  Purchase #6 $235.97   6.273%   $250.7724   $250.77   $250.75   $250.80  
  Purchase #7 $165.60   13.195%   $187.4509   $187.45   $187.45   $187.50  
  7 purchase totals = $1,216.28       $1,313.8764   $1,313.87   $1,313.90   $1,313.90