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 $241.67   11.294%   $268.9642   $268.96   $268.95   $269.00  
  Purchase #2 $171.88   4.476%   $179.5733   $179.57   $179.55   $179.60  
  Purchase #3 $187.73   9.706%   $205.9511   $205.95   $205.95   $206.00  
  Purchase #4 $240.32   6.291%   $255.4385   $255.44   $255.45   $255.40  
  Purchase #5 $197.81   13.146%   $223.8141   $223.81   $223.80   $223.80  
  Purchase #6 $143.63   4.234%   $149.7113   $149.71   $149.70   $149.70  
  Purchase #7 $65.62   10.258%   $72.3513   $72.35   $72.35   $72.40  
  7 purchase totals = $1,248.66       $1,355.8038   $1,355.79   $1,355.75   $1,355.90