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	$203.43	12.254%	$228.3583	$228.36	$228.35	$228.40
Purchase #2	$10.92	12.627%	$12.2989	$12.30	$12.30	$12.30
Purchase #3	$93.45	6.730%	$99.7392	$99.74	$99.75	$99.70
Purchase #4	$38.42	13.228%	$43.5022	$43.50	$43.50	$43.50
Purchase #5	$190.49	11.465%	$212.3297	$212.33	$212.35	$212.30
Purchase #6	$150.28	10.436%	$165.9632	$165.96	$165.95	$166.00
Purchase #7	$91.51	5.142%	$96.2154	$96.22	$96.20	$96.20
7 purchase totals =	$778.50		$858.4069	$858.41	$858.40	$858.40