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	$5.25	4.634%	$5.4933	$5.49	$5.50	$5.50
Purchase #2	$29.79	9.245%	$32.5441	$32.54	$32.55	$32.50
Purchase #3	$28.56	6.717%	$30.4784	$30.48	$30.50	$30.50
Purchase #4	$91.43	9.246%	$99.8836	$99.88	$99.90	$99.90
Purchase #5	$160.58	4.179%	$167.2906	$167.29	$167.30	$167.30
Purchase #6	$129.34	5.543%	$136.5093	$136.51	$136.50	$136.50
Purchase #7	$200.28	11.609%	$223.5305	$223.53	$223.55	$223.50
7 purchase totals =	$645.23		$695.7298	$695.72	$695.80	$695.70