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 $249.81   9.185%   $272.755   $272.76   $272.75   $272.80  
  Purchase #2 $116.72   11.679%   $130.3517   $130.35   $130.35   $130.40  
  Purchase #3 $96.36   13.409%   $109.2809   $109.28   $109.30   $109.30  
  Purchase #4 $161.81   3.686%   $167.7743   $167.77   $167.75   $167.80  
  Purchase #5 $178.53   10.747%   $197.7166   $197.72   $197.70   $197.70  
  Purchase #6 $172.85   7.378%   $185.6029   $185.60   $185.60   $185.60  
  Purchase #7 $185.29   8.463%   $200.9711   $200.97   $200.95   $201.00  
  7 purchase totals = $1,161.37       $1,264.4525   $1,264.45   $1,264.40   $1,264.60