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	$45.95	9.544%	$50.3355	$50.34	$50.35	$50.30
Purchase #2	$35.94	7.575%	$38.6625	$38.66	$38.65	$38.70
Purchase #3	$37.56	10.846%	$41.6338	$41.63	$41.65	$41.60
Purchase #4	$142.96	6.146%	$151.7463	$151.75	$151.75	$151.70
Purchase #5	$223.69	6.874%	$239.0665	$239.07	$239.05	$239.10
Purchase #6	$38.88	10.416%	$42.9297	$42.93	$42.95	$42.90
Purchase #7	$33.35	3.313%	$34.4549	$34.45	$34.45	$34.50
7 purchase totals =	$558.33		$598.8292	$598.83	$598.85	$598.80