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	$98.78	11.191%	$109.8345	$109.83	$109.85	$109.80
Purchase #2	$154.85	11.114%	$172.06	$172.06	$172.05	$172.10
Purchase #3	$7.66	4.168%	$7.9793	$7.98	$8.00	$8.00
Purchase #4	$156.79	8.334%	$169.8569	$169.86	$169.85	$169.90
Purchase #5	$224.54	12.735%	$253.1352	$253.14	$253.15	$253.10
Purchase #6	$92.39	13.764%	$105.1066	$105.11	$105.10	$105.10
Purchase #7	$28.49	6.268%	$30.2758	$30.28	$30.30	$30.30
7 purchase totals =	$763.50		$848.2483	$848.26	$848.30	$848.30