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	$77.47	3.105%	$79.8754	$79.88	$79.90	$79.90
Purchase #2	$173.47	4.300%	$180.9292	$180.93	$180.95	$180.90
Purchase #3	$115.61	10.264%	$127.4762	$127.48	$127.50	$127.50
Purchase #4	$51.48	7.761%	$55.4754	$55.48	$55.50	$55.50
Purchase #5	$157.31	4.788%	$164.842	$164.84	$164.85	$164.80
Purchase #6	$192.65	12.770%	$217.2514	$217.25	$217.25	$217.30
Purchase #7	$26.54	5.210%	$27.9227	$27.92	$27.90	$27.90
7 purchase totals =	$794.53		$853.7723	$853.78	$853.85	$853.80