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 $249.78   5.134%   $262.6037   $262.60   $262.60   $262.60  
  Purchase #2 $206.49   4.195%   $215.1523   $215.15   $215.15   $215.20  
  Purchase #3 $123.51   8.769%   $134.3406   $134.34   $134.35   $134.30  
  Purchase #4 $28.47   5.608%   $30.0666   $30.07   $30.05   $30.10  
  Purchase #5 $152.86   11.764%   $170.8425   $170.84   $170.85   $170.80  
  Purchase #6 $165.25   9.713%   $181.3007   $181.30   $181.30   $181.30  
  Purchase #7 $77.46   10.448%   $85.553   $85.55   $85.55   $85.60  
  7 purchase totals = $1,003.82       $1,079.8594   $1,079.85   $1,079.85   $1,079.90