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 $89.55   10.771%   $99.1954   $99.20   $99.20   $99.20  
  Purchase #2 $231.64   11.781%   $258.9295   $258.93   $258.95   $258.90  
  Purchase #3 $118.34   11.660%   $132.1384   $132.14   $132.15   $132.10  
  Purchase #4 $209.68   6.577%   $223.4707   $223.47   $223.45   $223.50  
  Purchase #5 $124.91   12.410%   $140.4113   $140.41   $140.40   $140.40  
  Purchase #6 $214.56   6.602%   $228.7253   $228.73   $228.75   $228.70  
  Purchase #7 $182.93   9.314%   $199.9681   $199.97   $199.95   $200.00  
  7 purchase totals = $1,171.61       $1,282.8387   $1,282.85   $1,282.85   $1,282.80