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 $173.54   5.592%   $183.2444   $183.24   $183.25   $183.20  
  Purchase #2 $228.45   11.466%   $254.6441   $254.64   $254.65   $254.60  
  Purchase #3 $217.62   11.475%   $242.5919   $242.59   $242.60   $242.60  
  Purchase #4 $152.65   11.527%   $170.246   $170.25   $170.25   $170.20  
  Purchase #5 $62.62   6.123%   $66.4542   $66.45   $66.45   $66.50  
  Purchase #6 $130.57   12.540%   $146.9435   $146.94   $146.95   $146.90  
  Purchase #7 $47.69   7.442%   $51.2391   $51.24   $51.25   $51.20  
  7 purchase totals = $1,013.14       $1,115.3632   $1,115.35   $1,115.40   $1,115.20