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 $66.97   12.842%   $75.5703   $75.57   $75.55   $75.60  
  Purchase #2 $131.43   4.577%   $137.4456   $137.45   $137.45   $137.40  
  Purchase #3 $168.95   10.367%   $186.465   $186.47   $186.45   $186.50  
  Purchase #4 $189.90   12.806%   $214.2186   $214.22   $214.20   $214.20  
  Purchase #5 $47.39   13.401%   $53.7407   $53.74   $53.75   $53.70  
  Purchase #6 $101.41   3.450%   $104.9086   $104.91   $104.90   $104.90  
  Purchase #7 $248.72   5.691%   $262.8747   $262.87   $262.85   $262.90  
  7 purchase totals = $954.77       $1,035.2235   $1,035.23   $1,035.15   $1,035.20