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 $249.66   6.605%   $266.15   $266.15   $266.15   $266.20  
  Purchase #2 $150.45   11.660%   $167.9925   $167.99   $168.00   $168.00  
  Purchase #3 $112.99   5.794%   $119.5366   $119.54   $119.55   $119.50  
  Purchase #4 $5.71   5.108%   $6.0017   $6.00   $6.00   $6.00  
  Purchase #5 $41.26   10.682%   $45.6674   $45.67   $45.65   $45.70  
  Purchase #6 $227.33   13.772%   $258.6379   $258.64   $258.65   $258.60  
  Purchase #7 $214.53   6.201%   $227.833   $227.83   $227.85   $227.80  
  7 purchase totals = $1,001.93       $1,091.8191   $1,091.82   $1,091.85   $1,091.80