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	$166.30	13.554%	$188.8403	$188.84	$188.85	$188.80
Purchase #2	$71.32	4.229%	$74.3361	$74.34	$74.35	$74.30
Purchase #3	$155.59	5.506%	$164.1568	$164.16	$164.15	$164.20
Purchase #4	$40.80	11.872%	$45.6438	$45.64	$45.65	$45.60
Purchase #5	$25.60	6.470%	$27.2563	$27.26	$27.25	$27.30
Purchase #6	$180.89	6.580%	$192.7926	$192.79	$192.80	$192.80
Purchase #7	$137.63	11.542%	$153.5153	$153.52	$153.50	$153.50
7 purchase totals =	$778.13		$846.5412	$846.55	$846.55	$846.50