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 $246.50   11.808%   $275.6067   $275.61   $275.60   $275.60  
  Purchase #2 $67.54   4.699%   $70.7137   $70.71   $70.70   $70.70  
  Purchase #3 $199.36   5.304%   $209.9341   $209.93   $209.95   $209.90  
  Purchase #4 $171.82   7.362%   $184.4694   $184.47   $184.45   $184.50  
  Purchase #5 $37.32   3.606%   $38.6658   $38.67   $38.65   $38.70  
  Purchase #6 $107.34   13.402%   $121.7257   $121.73   $121.75   $121.70  
  Purchase #7 $115.26   8.630%   $125.2069   $125.21   $125.20   $125.20  
  7 purchase totals = $945.14       $1,026.3223   $1,026.33   $1,026.30   $1,026.30