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 $212.25   11.285%   $236.2024   $236.20   $236.20   $236.20  
  Purchase #2 $202.71   8.723%   $220.3924   $220.39   $220.40   $220.40  
  Purchase #3 $57.29   13.861%   $65.231   $65.23   $65.25   $65.20  
  Purchase #4 $124.79   3.554%   $129.225   $129.23   $129.25   $129.20  
  Purchase #5 $60.62   9.649%   $66.4692   $66.47   $66.45   $66.50  
  Purchase #6 $224.83   7.141%   $240.8851   $240.89   $240.90   $240.90  
  Purchase #7 $125.95   5.519%   $132.9012   $132.90   $132.90   $132.90  
  7 purchase totals = $1,008.44       $1,091.3063   $1,091.31   $1,091.35   $1,091.30