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 $241.63   6.573%   $257.5123   $257.51   $257.50   $257.50  
  Purchase #2 $183.45   10.520%   $202.7489   $202.75   $202.75   $202.70  
  Purchase #3 $171.61   13.549%   $194.8614   $194.86   $194.85   $194.90  
  Purchase #4 $246.34   5.499%   $259.8862   $259.89   $259.90   $259.90  
  Purchase #5 $224.50   4.764%   $235.1952   $235.20   $235.20   $235.20  
  Purchase #6 $169.61   8.386%   $183.8335   $183.83   $183.85   $183.80  
  Purchase #7 $85.97   13.533%   $97.6043   $97.60   $97.60   $97.60  
  7 purchase totals = $1,323.11       $1,431.6418   $1,431.64   $1,431.65   $1,431.60