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	$133.39	11.373%	$148.5604	$148.56	$148.55	$148.60
Purchase #2	$181.30	6.738%	$193.516	$193.52	$193.50	$193.50
Purchase #3	$131.61	10.316%	$145.1869	$145.19	$145.20	$145.20
Purchase #4	$245.42	7.808%	$264.5824	$264.58	$264.60	$264.60
Purchase #5	$182.90	6.281%	$194.3879	$194.39	$194.40	$194.40
Purchase #6	$226.64	12.475%	$254.9133	$254.91	$254.90	$254.90
Purchase #7	$99.31	10.341%	$109.5796	$109.58	$109.60	$109.60
7 purchase totals =	$1,200.57		$1,310.7265	$1,310.73	$1,310.75	$1,310.80