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	$116.78	3.191%	$120.5064	$120.51	$120.50	$120.50
Purchase #2	$92.64	8.582%	$100.5904	$100.59	$100.60	$100.60
Purchase #3	$42.74	10.702%	$47.314	$47.31	$47.30	$47.30
Purchase #4	$33.98	8.819%	$36.9767	$36.98	$37.00	$37.00
Purchase #5	$48.84	8.633%	$53.0564	$53.06	$53.05	$53.10
Purchase #6	$153.27	8.511%	$166.3148	$166.31	$166.30	$166.30
Purchase #7	$17.76	11.219%	$19.7525	$19.75	$19.75	$19.80
7 purchase totals =	$506.01		$544.5112	$544.51	$544.50	$544.60