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 $216.46   12.764%   $244.089   $244.09   $244.10   $244.10  
  Purchase #2 $121.45   12.149%   $136.205   $136.21   $136.20   $136.20  
  Purchase #3 $192.40   11.359%   $214.2547   $214.25   $214.25   $214.30  
  Purchase #4 $92.59   12.616%   $104.2712   $104.27   $104.25   $104.30  
  Purchase #5 $196.99   9.454%   $215.6134   $215.61   $215.60   $215.60  
  Purchase #6 $101.65   5.185%   $106.9206   $106.92   $106.90   $106.90  
  Purchase #7 $238.51   3.330%   $246.4524   $246.45   $246.45   $246.50  
  7 purchase totals = $1,160.05       $1,267.8063   $1,267.80   $1,267.75   $1,267.90