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	$6.59	13.138%	$7.4558	$7.46	$7.45	$7.50
Purchase #2	$102.52	8.385%	$111.1163	$111.12	$111.10	$111.10
Purchase #3	$41.45	9.230%	$45.2758	$45.28	$45.30	$45.30
Purchase #4	$198.68	11.687%	$221.8997	$221.90	$221.90	$221.90
Purchase #5	$7.69	4.774%	$8.0571	$8.06	$8.05	$8.10
Purchase #6	$235.82	12.129%	$264.4226	$264.42	$264.40	$264.40
Purchase #7	$31.85	13.494%	$36.1478	$36.15	$36.15	$36.10
7 purchase totals =	$624.60		$694.3751	$694.39	$694.35	$694.40