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 $246.71   7.431%   $265.043   $265.04   $265.05   $265.00  
  Purchase #2 $203.33   4.189%   $211.8475   $211.85   $211.85   $211.80  
  Purchase #3 $7.32   3.139%   $7.5498   $7.55   $7.55   $7.50  
  Purchase #4 $21.76   10.756%   $24.1005   $24.10   $24.10   $24.10  
  Purchase #5 $90.62   8.653%   $98.4613   $98.46   $98.45   $98.50  
  Purchase #6 $53.33   3.207%   $55.0403   $55.04   $55.05   $55.00  
  Purchase #7 $200.32   3.819%   $207.9702   $207.97   $207.95   $208.00  
  7 purchase totals = $823.39       $870.0126   $870.01   $870.00   $869.90