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	$194.36	11.432%	$216.5792	$216.58	$216.60	$216.60
Purchase #2	$242.44	13.512%	$275.1985	$275.20	$275.20	$275.20
Purchase #3	$109.66	9.584%	$120.1698	$120.17	$120.15	$120.20
Purchase #4	$72.99	7.848%	$78.7183	$78.72	$78.70	$78.70
Purchase #5	$242.74	8.818%	$264.1448	$264.14	$264.15	$264.10
Purchase #6	$225.37	7.461%	$242.1849	$242.18	$242.20	$242.20
Purchase #7	$59.32	3.848%	$61.6026	$61.60	$61.60	$61.60
7 purchase totals =	$1,146.88		$1,258.5981	$1,258.59	$1,258.60	$1,258.60