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 $212.45   11.102%   $236.0362   $236.04   $236.05   $236.00  
  Purchase #2 $205.62   7.435%   $220.9078   $220.91   $220.90   $220.90  
  Purchase #3 $156.60   13.242%   $177.337   $177.34   $177.35   $177.30  
  Purchase #4 $124.57   5.672%   $131.6356   $131.64   $131.65   $131.60  
  Purchase #5 $127.31   4.515%   $133.058   $133.06   $133.05   $133.10  
  Purchase #6 $205.91   4.378%   $214.9247   $214.92   $214.90   $214.90  
  Purchase #7 $198.63   11.739%   $221.9472   $221.95   $221.95   $221.90  
  7 purchase totals = $1,231.09       $1,335.8465   $1,335.86   $1,335.85   $1,335.70