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 $240.32   9.524%   $263.2081   $263.21   $263.20   $263.20  
  Purchase #2 $114.87   5.283%   $120.9386   $120.94   $120.95   $120.90  
  Purchase #3 $205.84   4.439%   $214.9772   $214.98   $215.00   $215.00  
  Purchase #4 $58.43   3.318%   $60.3687   $60.37   $60.35   $60.40  
  Purchase #5 $69.40   7.524%   $74.6217   $74.62   $74.60   $74.60  
  Purchase #6 $145.83   10.574%   $161.2501   $161.25   $161.25   $161.30  
  Purchase #7 $121.33   3.475%   $125.5462   $125.55   $125.55   $125.50  
  7 purchase totals = $956.02       $1,020.9106   $1,020.92   $1,020.90   $1,020.90