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	$26.50	9.499%	$29.0172	$29.02	$29.00	$29.00
Purchase #2	$58.82	3.144%	$60.6693	$60.67	$60.65	$60.70
Purchase #3	$29.46	6.141%	$31.2691	$31.27	$31.25	$31.30
Purchase #4	$58.40	5.762%	$61.765	$61.77	$61.75	$61.80
Purchase #5	$37.56	7.595%	$40.4127	$40.41	$40.40	$40.40
Purchase #6	$20.57	7.535%	$22.1199	$22.12	$22.10	$22.10
Purchase #7	$150.30	12.374%	$168.8981	$168.90	$168.90	$168.90
7 purchase totals =	$381.61		$414.1513	$414.16	$414.05	$414.20