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	$78.27	3.821%	$81.2607	$81.26	$81.25	$81.30
Purchase #2	$92.28	13.684%	$104.9076	$104.91	$104.90	$104.90
Purchase #3	$46.40	3.251%	$47.9085	$47.91	$47.90	$47.90
Purchase #4	$33.62	11.716%	$37.5589	$37.56	$37.55	$37.60
Purchase #5	$212.83	3.223%	$219.6895	$219.69	$219.70	$219.70
Purchase #6	$84.28	5.794%	$89.1632	$89.16	$89.15	$89.20
Purchase #7	$17.51	13.384%	$19.8535	$19.85	$19.85	$19.90
7 purchase totals =	$565.19		$600.3419	$600.34	$600.30	$600.50