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 $205.87   4.148%   $214.4095   $214.41   $214.40   $214.40  
  Purchase #2 $193.38   11.675%   $215.9571   $215.96   $215.95   $216.00  
  Purchase #3 $239.54   7.443%   $257.369   $257.37   $257.35   $257.40  
  Purchase #4 $184.80   6.873%   $197.5013   $197.50   $197.50   $197.50  
  Purchase #5 $246.37   11.260%   $274.1113   $274.11   $274.10   $274.10  
  Purchase #6 $8.44   12.651%   $9.5077   $9.51   $9.50   $9.50  
  Purchase #7 $122.73   8.494%   $133.1547   $133.15   $133.15   $133.20  
  7 purchase totals = $1,201.13       $1,302.0106   $1,302.01   $1,301.95   $1,302.10