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	$190.91	3.338%	$197.2826	$197.28	$197.30	$197.30
Purchase #2	$211.89	5.529%	$223.6054	$223.61	$223.60	$223.60
Purchase #3	$243.64	8.483%	$264.308	$264.31	$264.30	$264.30
Purchase #4	$78.88	5.230%	$83.0054	$83.01	$83.00	$83.00
Purchase #5	$179.69	4.728%	$188.1857	$188.19	$188.20	$188.20
Purchase #6	$66.41	8.764%	$72.2302	$72.23	$72.25	$72.20
Purchase #7	$97.91	13.463%	$111.0916	$111.09	$111.10	$111.10
7 purchase totals =	$1,069.33		$1,139.7089	$1,139.72	$1,139.75	$1,139.70