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 $127.34   6.256%   $135.3064   $135.31   $135.30   $135.30  
  Purchase #2 $169.74   6.337%   $180.4964   $180.50   $180.50   $180.50  
  Purchase #3 $231.33   13.589%   $262.7654   $262.77   $262.75   $262.80  
  Purchase #4 $44.39   9.509%   $48.611   $48.61   $48.60   $48.60  
  Purchase #5 $85.49   11.167%   $95.0367   $95.04   $95.05   $95.00  
  Purchase #6 $12.67   4.281%   $13.2124   $13.21   $13.20   $13.20  
  Purchase #7 $241.73   6.419%   $257.2466   $257.25   $257.25   $257.20  
  7 purchase totals = $912.69       $992.6749   $992.69   $992.65   $992.60