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	$223.48	7.433%	$240.0913	$240.09	$240.10	$240.10
Purchase #2	$130.33	10.621%	$144.1723	$144.17	$144.15	$144.20
Purchase #3	$71.40	9.333%	$78.0638	$78.06	$78.05	$78.10
Purchase #4	$179.51	8.450%	$194.6786	$194.68	$194.70	$194.70
Purchase #5	$208.26	7.362%	$223.5921	$223.59	$223.60	$223.60
Purchase #6	$179.60	3.290%	$185.5088	$185.51	$185.50	$185.50
Purchase #7	$46.33	10.393%	$51.1451	$51.15	$51.15	$51.10
7 purchase totals =	$1,038.91		$1,117.2520	$1,117.25	$1,117.25	$1,117.30