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	$121.69	4.827%	$127.564	$127.56	$127.55	$127.60
Purchase #2	$16.41	6.698%	$17.5091	$17.51	$17.50	$17.50
Purchase #3	$120.47	9.330%	$131.7099	$131.71	$131.70	$131.70
Purchase #4	$240.31	10.234%	$264.9033	$264.90	$264.90	$264.90
Purchase #5	$51.35	13.252%	$58.1549	$58.15	$58.15	$58.20
Purchase #6	$124.69	10.155%	$137.3523	$137.35	$137.35	$137.40
Purchase #7	$155.97	13.170%	$176.5112	$176.51	$176.50	$176.50
7 purchase totals =	$830.89		$913.7047	$913.69	$913.65	$913.80