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	$134.31	13.402%	$152.3102	$152.31	$152.30	$152.30
Purchase #2	$220.44	9.196%	$240.7117	$240.71	$240.70	$240.70
Purchase #3	$248.64	12.362%	$279.3769	$279.38	$279.40	$279.40
Purchase #4	$125.86	3.492%	$130.255	$130.26	$130.25	$130.30
Purchase #5	$89.92	4.298%	$93.7848	$93.78	$93.80	$93.80
Purchase #6	$65.83	4.733%	$68.9457	$68.95	$68.95	$68.90
Purchase #7	$129.51	4.129%	$134.8575	$134.86	$134.85	$134.90
7 purchase totals =	$1,014.51		$1,100.2418	$1,100.25	$1,100.25	$1,100.30