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 $236.58   9.583%   $259.2515   $259.25   $259.25   $259.30  
  Purchase #2 $58.76   5.455%   $61.9654   $61.97   $61.95   $62.00  
  Purchase #3 $225.94   11.517%   $251.9615   $251.96   $251.95   $252.00  
  Purchase #4 $58.32   9.800%   $64.0354   $64.04   $64.05   $64.00  
  Purchase #5 $118.77   11.588%   $132.5331   $132.53   $132.55   $132.50  
  Purchase #6 $241.53   4.609%   $252.6621   $252.66   $252.65   $252.70  
  Purchase #7 $47.87   6.540%   $51.0007   $51.00   $51.00   $51.00  
  7 purchase totals = $987.77       $1,073.4097   $1,073.41   $1,073.40   $1,073.50