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	$173.65	3.400%	$179.5541	$179.55	$179.55	$179.60
Purchase #2	$185.33	10.524%	$204.8341	$204.83	$204.85	$204.80
Purchase #3	$124.50	11.860%	$139.2657	$139.27	$139.25	$139.30
Purchase #4	$37.77	5.173%	$39.7238	$39.72	$39.70	$39.70
Purchase #5	$79.31	13.812%	$90.2643	$90.26	$90.25	$90.30
Purchase #6	$215.53	13.268%	$244.1265	$244.13	$244.15	$244.10
Purchase #7	$102.81	3.607%	$106.5184	$106.52	$106.50	$106.50
7 purchase totals =	$918.90		$1,004.2869	$1,004.28	$1,004.25	$1,004.30