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 $201.91   12.501%   $227.1508   $227.15   $227.15   $227.20  
  Purchase #2 $246.93   11.752%   $275.9492   $275.95   $275.95   $275.90  
  Purchase #3 $71.39   8.309%   $77.3218   $77.32   $77.30   $77.30  
  Purchase #4 $190.88   9.157%   $208.3589   $208.36   $208.35   $208.40  
  Purchase #5 $137.79   5.632%   $145.5503   $145.55   $145.55   $145.60  
  Purchase #6 $125.37   5.563%   $132.3443   $132.34   $132.35   $132.30  
  Purchase #7 $183.68   5.833%   $194.3941   $194.39   $194.40   $194.40  
  7 purchase totals = $1,157.95       $1,261.0694   $1,261.06   $1,261.05   $1,261.10