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 $24.43   5.359%   $25.7392   $25.74   $25.75   $25.70  
  Purchase #2 $205.94   11.288%   $229.1865   $229.19   $229.20   $229.20  
  Purchase #3 $215.35   7.245%   $230.9521   $230.95   $230.95   $231.00  
  Purchase #4 $32.83   4.161%   $34.1961   $34.20   $34.20   $34.20  
  Purchase #5 $225.70   11.526%   $251.7142   $251.71   $251.70   $251.70  
  Purchase #6 $180.43   10.627%   $199.6043   $199.60   $199.60   $199.60  
  Purchase #7 $234.96   10.240%   $259.0199   $259.02   $259.00   $259.00  
  7 purchase totals = $1,119.64       $1,230.4123   $1,230.41   $1,230.40   $1,230.40