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	$69.33	11.573%	$77.3536	$77.35	$77.35	$77.40
Purchase #2	$133.44	8.226%	$144.4168	$144.42	$144.40	$144.40
Purchase #3	$148.50	7.765%	$160.031	$160.03	$160.05	$160.00
Purchase #4	$96.35	8.809%	$104.8375	$104.84	$104.85	$104.80
Purchase #5	$24.89	10.846%	$27.5896	$27.59	$27.60	$27.60
Purchase #6	$36.33	7.762%	$39.1499	$39.15	$39.15	$39.10
Purchase #7	$43.59	3.785%	$45.2399	$45.24	$45.25	$45.20
7 purchase totals =	$552.43		$598.6183	$598.62	$598.65	$598.50