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 $65.30   6.337%   $69.4381   $69.44   $69.45   $69.40  
  Purchase #2 $218.32   10.145%   $240.4686   $240.47   $240.45   $240.50  
  Purchase #3 $236.73   6.370%   $251.8097   $251.81   $251.80   $251.80  
  Purchase #4 $44.81   4.234%   $46.7073   $46.71   $46.70   $46.70  
  Purchase #5 $89.74   8.599%   $97.4567   $97.46   $97.45   $97.50  
  Purchase #6 $187.78   13.189%   $212.5463   $212.55   $212.55   $212.50  
  Purchase #7 $112.30   13.720%   $127.7076   $127.71   $127.70   $127.70  
  7 purchase totals = $954.98       $1,046.1343   $1,046.15   $1,046.10   $1,046.10