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	$76.56	8.287%	$82.9045	$82.90	$82.90	$82.90
Purchase #2	$31.99	11.472%	$35.6599	$35.66	$35.65	$35.70
Purchase #3	$170.69	9.637%	$187.1394	$187.14	$187.15	$187.10
Purchase #4	$150.87	6.280%	$160.3446	$160.34	$160.35	$160.30
Purchase #5	$118.39	7.500%	$127.2693	$127.27	$127.25	$127.30
Purchase #6	$134.48	5.643%	$142.0687	$142.07	$142.05	$142.10
Purchase #7	$78.75	12.415%	$88.5268	$88.53	$88.55	$88.50
7 purchase totals =	$761.73		$823.9132	$823.91	$823.90	$823.90