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	$50.78	6.676%	$54.1701	$54.17	$54.15	$54.20
Purchase #2	$150.51	13.615%	$171.0019	$171.00	$171.00	$171.00
Purchase #3	$173.85	7.806%	$187.4207	$187.42	$187.40	$187.40
Purchase #4	$113.64	13.474%	$128.9519	$128.95	$128.95	$129.00
Purchase #5	$172.27	11.397%	$191.9036	$191.90	$191.90	$191.90
Purchase #6	$225.76	10.552%	$249.5822	$249.58	$249.60	$249.60
Purchase #7	$81.44	10.165%	$89.7184	$89.72	$89.70	$89.70
7 purchase totals =	$968.25		$1,072.7488	$1,072.74	$1,072.70	$1,072.80