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	$159.74	12.318%	$179.4168	$179.42	$179.40	$179.40
Purchase #2	$55.39	6.521%	$59.002	$59.00	$59.00	$59.00
Purchase #3	$95.57	6.824%	$102.0917	$102.09	$102.10	$102.10
Purchase #4	$147.80	11.834%	$165.2907	$165.29	$165.30	$165.30
Purchase #5	$244.34	9.287%	$267.0319	$267.03	$267.05	$267.00
Purchase #6	$24.96	11.848%	$27.9173	$27.92	$27.90	$27.90
Purchase #7	$109.62	4.608%	$114.6713	$114.67	$114.65	$114.70
7 purchase totals =	$837.42		$915.4217	$915.42	$915.40	$915.40