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	$210.33	13.323%	$238.3523	$238.35	$238.35	$238.40
Purchase #2	$201.84	10.874%	$223.7881	$223.79	$223.80	$223.80
Purchase #3	$99.55	11.734%	$111.2312	$111.23	$111.25	$111.20
Purchase #4	$26.74	6.478%	$28.4722	$28.47	$28.45	$28.50
Purchase #5	$105.54	3.410%	$109.1389	$109.14	$109.15	$109.10
Purchase #6	$175.57	4.793%	$183.9851	$183.99	$184.00	$184.00
Purchase #7	$38.49	8.747%	$41.8567	$41.86	$41.85	$41.90
7 purchase totals =	$858.06		$936.8245	$936.83	$936.85	$936.90