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	$78.39	8.488%	$85.0437	$85.04	$85.05	$85.00
Purchase #2	$179.36	3.823%	$186.2169	$186.22	$186.20	$186.20
Purchase #3	$229.48	13.804%	$261.1574	$261.16	$261.15	$261.20
Purchase #4	$49.93	11.855%	$55.8492	$55.85	$55.85	$55.80
Purchase #5	$73.90	6.483%	$78.6909	$78.69	$78.70	$78.70
Purchase #6	$16.92	10.689%	$18.7286	$18.73	$18.75	$18.70
Purchase #7	$149.31	6.272%	$158.6747	$158.67	$158.65	$158.70
7 purchase totals =	$777.29		$844.3614	$844.36	$844.35	$844.30