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	$199.98	4.575%	$209.1291	$209.13	$209.15	$209.10
Purchase #2	$111.27	9.184%	$121.489	$121.49	$121.50	$121.50
Purchase #3	$35.50	13.420%	$40.2641	$40.26	$40.25	$40.30
Purchase #4	$91.56	4.697%	$95.8606	$95.86	$95.85	$95.90
Purchase #5	$139.98	5.217%	$147.2828	$147.28	$147.30	$147.30
Purchase #6	$152.88	13.361%	$173.3063	$173.31	$173.30	$173.30
Purchase #7	$51.56	9.563%	$56.4907	$56.49	$56.50	$56.50
7 purchase totals =	$782.73		$843.8226	$843.82	$843.85	$843.90