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	$42.75	5.327%	$45.0273	$45.03	$45.05	$45.00
Purchase #2	$93.95	7.495%	$100.9916	$100.99	$101.00	$101.00
Purchase #3	$165.58	10.833%	$183.5173	$183.52	$183.50	$183.50
Purchase #4	$69.33	13.711%	$78.8358	$78.84	$78.85	$78.80
Purchase #5	$187.87	10.793%	$208.1468	$208.15	$208.15	$208.10
Purchase #6	$149.55	6.263%	$158.9163	$158.92	$158.90	$158.90
Purchase #7	$147.70	3.641%	$153.0778	$153.08	$153.10	$153.10
7 purchase totals =	$856.73		$928.5129	$928.53	$928.55	$928.40