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	$183.39	9.342%	$200.5223	$200.52	$200.50	$200.50
Purchase #2	$124.61	12.282%	$139.9146	$139.91	$139.90	$139.90
Purchase #3	$138.50	9.733%	$151.9802	$151.98	$152.00	$152.00
Purchase #4	$88.83	11.830%	$99.3386	$99.34	$99.35	$99.30
Purchase #5	$185.29	9.297%	$202.5164	$202.52	$202.50	$202.50
Purchase #6	$174.85	11.190%	$194.4157	$194.42	$194.40	$194.40
Purchase #7	$167.97	13.795%	$191.1415	$191.14	$191.15	$191.10
7 purchase totals =	$1,063.44		$1,179.8293	$1,179.83	$1,179.80	$1,179.70