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	$84.58	6.290%	$89.9001	$89.90	$89.90	$89.90
Purchase #2	$60.73	7.518%	$65.2957	$65.30	$65.30	$65.30
Purchase #3	$227.91	11.676%	$254.5208	$254.52	$254.50	$254.50
Purchase #4	$22.36	9.395%	$24.4607	$24.46	$24.45	$24.50
Purchase #5	$231.88	13.352%	$262.8406	$262.84	$262.85	$262.80
Purchase #6	$163.25	10.769%	$180.8304	$180.83	$180.85	$180.80
Purchase #7	$202.30	8.447%	$219.3883	$219.39	$219.40	$219.40
7 purchase totals =	$993.01		$1,097.2366	$1,097.24	$1,097.25	$1,097.20