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 $248.98   13.638%   $282.9359   $282.94   $282.95   $282.90  
  Purchase #2 $13.32   4.426%   $13.9095   $13.91   $13.90   $13.90  
  Purchase #3 $95.43   7.654%   $102.7342   $102.73   $102.75   $102.70  
  Purchase #4 $205.38   3.743%   $213.0674   $213.07   $213.05   $213.10  
  Purchase #5 $148.81   6.275%   $158.1478   $158.15   $158.15   $158.10  
  Purchase #6 $117.73   4.788%   $123.3669   $123.37   $123.35   $123.40  
  Purchase #7 $58.79   12.183%   $65.9524   $65.95   $65.95   $66.00  
  7 purchase totals = $888.44       $960.1141   $960.12   $960.10   $960.10