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	$70.74	7.485%	$76.0349	$76.03	$76.05	$76.00
Purchase #2	$43.84	12.456%	$49.3007	$49.30	$49.30	$49.30
Purchase #3	$63.58	13.352%	$72.0692	$72.07	$72.05	$72.10
Purchase #4	$47.83	7.621%	$51.4751	$51.48	$51.50	$51.50
Purchase #5	$88.39	12.321%	$99.2805	$99.28	$99.30	$99.30
Purchase #6	$118.27	8.650%	$128.5004	$128.50	$128.50	$128.50
Purchase #7	$30.37	4.793%	$31.8256	$31.83	$31.85	$31.80
7 purchase totals =	$463.02		$508.4864	$508.49	$508.55	$508.50