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 $239.53   13.829%   $272.6546   $272.65   $272.65   $272.70  
  Purchase #2 $177.38   3.601%   $183.7675   $183.77   $183.75   $183.80  
  Purchase #3 $62.65   12.723%   $70.621   $70.62   $70.60   $70.60  
  Purchase #4 $86.32   12.872%   $97.4311   $97.43   $97.45   $97.40  
  Purchase #5 $188.80   13.868%   $214.9828   $214.98   $215.00   $215.00  
  Purchase #6 $88.89   7.317%   $95.3941   $95.39   $95.40   $95.40  
  Purchase #7 $242.75   12.481%   $273.0476   $273.05   $273.05   $273.00  
  7 purchase totals = $1,086.32       $1,207.8987   $1,207.89   $1,207.90   $1,207.90