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 $225.25   11.210%   $250.5005   $250.50   $250.50   $250.50  
  Purchase #2 $148.79   10.648%   $164.6332   $164.63   $164.65   $164.60  
  Purchase #3 $38.85   6.525%   $41.385   $41.39   $41.40   $41.40  
  Purchase #4 $95.99   6.598%   $102.3234   $102.32   $102.30   $102.30  
  Purchase #5 $88.25   5.458%   $93.0667   $93.07   $93.05   $93.10  
  Purchase #6 $156.35   3.376%   $161.6284   $161.63   $161.65   $161.60  
  Purchase #7 $124.35   6.348%   $132.2437   $132.24   $132.25   $132.20  
  7 purchase totals = $877.83       $945.7809   $945.78   $945.80   $945.70