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 $207.69   11.867%   $232.3366   $232.34   $232.35   $232.30  
  Purchase #2 $162.74   6.576%   $173.4418   $173.44   $173.45   $173.40  
  Purchase #3 $58.73   6.466%   $62.5275   $62.53   $62.55   $62.50  
  Purchase #4 $63.70   8.571%   $69.1597   $69.16   $69.15   $69.20  
  Purchase #5 $8.48   8.742%   $9.2213   $9.22   $9.20   $9.20  
  Purchase #6 $68.89   8.319%   $74.621   $74.62   $74.60   $74.60  
  Purchase #7 $134.42   13.840%   $153.0237   $153.02   $153.00   $153.00  
  7 purchase totals = $704.65       $774.3316   $774.33   $774.30   $774.20