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	$18.65	11.466%	$20.7884	$20.79	$20.80	$20.80
Purchase #2	$45.69	10.410%	$50.4463	$50.45	$50.45	$50.40
Purchase #3	$54.27	8.505%	$58.8857	$58.89	$58.90	$58.90
Purchase #4	$199.28	11.681%	$222.5579	$222.56	$222.55	$222.60
Purchase #5	$55.35	4.280%	$57.719	$57.72	$57.70	$57.70
Purchase #6	$231.74	6.211%	$246.1334	$246.13	$246.15	$246.10
Purchase #7	$182.41	5.476%	$192.3988	$192.40	$192.40	$192.40
7 purchase totals =	$787.39		$848.9295	$848.94	$848.95	$848.90