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 $226.97   3.194%   $234.2194   $234.22   $234.20   $234.20  
  Purchase #2 $82.60   11.828%   $92.3699   $92.37   $92.35   $92.40  
  Purchase #3 $6.58   12.745%   $7.4186   $7.42   $7.40   $7.40  
  Purchase #4 $27.37   6.759%   $29.2199   $29.22   $29.20   $29.20  
  Purchase #5 $16.82   3.749%   $17.4506   $17.45   $17.45   $17.50  
  Purchase #6 $246.55   6.505%   $262.5881   $262.59   $262.60   $262.60  
  Purchase #7 $178.81   7.538%   $192.2887   $192.29   $192.30   $192.30  
  7 purchase totals = $785.70       $835.5552   $835.56   $835.50   $835.60