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 $114.36   13.311%   $129.5825   $129.58   $129.60   $129.60  
  Purchase #2 $249.90   6.303%   $265.6512   $265.65   $265.65   $265.70  
  Purchase #3 $21.40   5.325%   $22.5396   $22.54   $22.55   $22.50  
  Purchase #4 $242.64   8.619%   $263.5531   $263.55   $263.55   $263.60  
  Purchase #5 $19.49   6.487%   $20.7543   $20.75   $20.75   $20.80  
  Purchase #6 $89.49   9.348%   $97.8555   $97.86   $97.85   $97.90  
  Purchase #7 $120.95   3.849%   $125.6054   $125.61   $125.60   $125.60  
  7 purchase totals = $858.23       $925.5416   $925.54   $925.55   $925.70