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 $232.96   5.818%   $246.5136   $246.51   $246.50   $246.50  
  Purchase #2 $241.69   8.264%   $261.6633   $261.66   $261.65   $261.70  
  Purchase #3 $225.30   9.282%   $246.2123   $246.21   $246.20   $246.20  
  Purchase #4 $248.68   8.321%   $269.3727   $269.37   $269.35   $269.40  
  Purchase #5 $241.25   11.194%   $268.2555   $268.26   $268.25   $268.30  
  Purchase #6 $144.86   13.310%   $164.1409   $164.14   $164.15   $164.10  
  Purchase #7 $181.92   12.471%   $204.6072   $204.61   $204.60   $204.60  
  7 purchase totals = $1,516.66       $1,660.7655   $1,660.76   $1,660.70   $1,660.80