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	$165.76	8.705%	$180.1894	$180.19	$180.20	$180.20
Purchase #2	$56.80	8.819%	$61.8092	$61.81	$61.80	$61.80
Purchase #3	$48.37	12.151%	$54.2474	$54.25	$54.25	$54.20
Purchase #4	$146.57	8.700%	$159.3216	$159.32	$159.30	$159.30
Purchase #5	$43.72	3.694%	$45.335	$45.34	$45.35	$45.30
Purchase #6	$218.84	10.551%	$241.9298	$241.93	$241.95	$241.90
Purchase #7	$109.65	3.693%	$113.6994	$113.70	$113.70	$113.70
7 purchase totals =	$789.71		$856.5318	$856.54	$856.55	$856.40