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 $225.82   3.451%   $233.613   $233.61   $233.60   $233.60  
  Purchase #2 $207.45   10.843%   $229.9438   $229.94   $229.95   $229.90  
  Purchase #3 $109.42   8.724%   $118.9658   $118.97   $118.95   $119.00  
  Purchase #4 $117.65   13.776%   $133.8575   $133.86   $133.85   $133.90  
  Purchase #5 $104.84   4.293%   $109.3408   $109.34   $109.35   $109.30  
  Purchase #6 $42.60   9.568%   $46.676   $46.68   $46.70   $46.70  
  Purchase #7 $118.92   4.761%   $124.5818   $124.58   $124.60   $124.60  
  7 purchase totals = $926.70       $996.9787   $996.98   $997.00   $997.00