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	$30.54	7.711%	$32.8949	$32.89	$32.90	$32.90
Purchase #2	$98.82	7.454%	$106.186	$106.19	$106.20	$106.20
Purchase #3	$15.95	10.738%	$17.6627	$17.66	$17.65	$17.70
Purchase #4	$151.65	11.387%	$168.9184	$168.92	$168.90	$168.90
Purchase #5	$151.92	6.716%	$162.1229	$162.12	$162.10	$162.10
Purchase #6	$204.52	8.303%	$221.5013	$221.50	$221.50	$221.50
Purchase #7	$53.39	7.259%	$57.2656	$57.27	$57.25	$57.30
7 purchase totals =	$706.79		$766.5518	$766.55	$766.50	$766.60