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 $6.90   9.542%   $7.5584   $7.56   $7.55   $7.60  
  Purchase #2 $102.66   3.723%   $106.482   $106.48   $106.50   $106.50  
  Purchase #3 $129.99   11.719%   $145.2235   $145.22   $145.20   $145.20  
  Purchase #4 $249.50   9.511%   $273.2299   $273.23   $273.25   $273.20  
  Purchase #5 $118.62   11.616%   $132.3989   $132.40   $132.40   $132.40  
  Purchase #6 $77.63   6.268%   $82.4958   $82.50   $82.50   $82.50  
  Purchase #7 $119.51   9.338%   $130.6698   $130.67   $130.65   $130.70  
  7 purchase totals = $804.81       $878.0583   $878.06   $878.05   $878.10