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 $170.59   6.852%   $182.2788   $182.28   $182.30   $182.30  
  Purchase #2 $52.33   11.374%   $58.282   $58.28   $58.30   $58.30  
  Purchase #3 $192.54   7.387%   $206.7629   $206.76   $206.75   $206.80  
  Purchase #4 $246.35   5.533%   $259.9805   $259.98   $260.00   $260.00  
  Purchase #5 $108.54   4.328%   $113.2376   $113.24   $113.25   $113.20  
  Purchase #6 $239.84   11.727%   $267.966   $267.97   $267.95   $268.00  
  Purchase #7 $154.28   4.689%   $161.5142   $161.51   $161.50   $161.50  
  7 purchase totals = $1,164.47       $1,250.0220   $1,250.02   $1,250.05   $1,250.10