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	$63.40	11.425%	$70.6435	$70.64	$70.65	$70.60
Purchase #2	$93.46	13.265%	$105.8575	$105.86	$105.85	$105.90
Purchase #3	$53.78	6.436%	$57.2413	$57.24	$57.25	$57.20
Purchase #4	$129.73	8.485%	$140.7376	$140.74	$140.75	$140.70
Purchase #5	$99.77	3.570%	$103.3318	$103.33	$103.35	$103.30
Purchase #6	$156.26	7.534%	$168.0326	$168.03	$168.05	$168.00
Purchase #7	$113.77	9.411%	$124.4769	$124.48	$124.50	$124.50
7 purchase totals =	$710.17		$770.3212	$770.32	$770.40	$770.20