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	$91.67	8.162%	$99.1521	$99.15	$99.15	$99.20
Purchase #2	$131.94	5.433%	$139.1083	$139.11	$139.10	$139.10
Purchase #3	$174.87	9.214%	$190.9825	$190.98	$191.00	$191.00
Purchase #4	$36.59	10.305%	$40.3606	$40.36	$40.35	$40.40
Purchase #5	$111.97	11.680%	$125.0481	$125.05	$125.05	$125.00
Purchase #6	$82.70	10.569%	$91.4406	$91.44	$91.45	$91.40
Purchase #7	$32.39	10.588%	$35.8195	$35.82	$35.80	$35.80
7 purchase totals =	$662.13		$721.9117	$721.91	$721.90	$721.90