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	$111.96	7.438%	$120.2876	$120.29	$120.30	$120.30
Purchase #2	$50.62	9.227%	$55.2907	$55.29	$55.30	$55.30
Purchase #3	$92.56	7.872%	$99.8463	$99.85	$99.85	$99.80
Purchase #4	$228.96	11.599%	$255.5171	$255.52	$255.50	$255.50
Purchase #5	$192.75	6.444%	$205.1708	$205.17	$205.15	$205.20
Purchase #6	$198.85	11.794%	$222.3024	$222.30	$222.30	$222.30
Purchase #7	$26.98	5.201%	$28.3832	$28.38	$28.40	$28.40
7 purchase totals =	$902.68		$986.7981	$986.80	$986.80	$986.80