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 $249.56   7.646%   $268.6414   $268.64   $268.65   $268.60  
  Purchase #2 $244.87   3.676%   $253.8714   $253.87   $253.85   $253.90  
  Purchase #3 $109.27   13.530%   $124.0542   $124.05   $124.05   $124.10  
  Purchase #4 $160.38   5.185%   $168.6957   $168.70   $168.70   $168.70  
  Purchase #5 $66.50   8.737%   $72.3101   $72.31   $72.30   $72.30  
  Purchase #6 $237.62   9.190%   $259.4573   $259.46   $259.45   $259.50  
  Purchase #7 $245.42   9.770%   $269.3975   $269.40   $269.40   $269.40  
  7 purchase totals = $1,313.62       $1,416.4276   $1,416.43   $1,416.40   $1,416.50