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 $231.60   9.129%   $252.7428   $252.74   $252.75   $252.70  
  Purchase #2 $54.97   11.389%   $61.2305   $61.23   $61.25   $61.20  
  Purchase #3 $162.68   6.684%   $173.5535   $173.55   $173.55   $173.60  
  Purchase #4 $99.99   13.138%   $113.1267   $113.13   $113.15   $113.10  
  Purchase #5 $59.80   8.553%   $64.9147   $64.91   $64.90   $64.90  
  Purchase #6 $162.28   5.342%   $170.949   $170.95   $170.95   $170.90  
  Purchase #7 $188.75   13.216%   $213.6952   $213.70   $213.70   $213.70  
  7 purchase totals = $960.07       $1,050.2124   $1,050.21   $1,050.25   $1,050.10