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	$155.88	7.381%	$167.3855	$167.39	$167.40	$167.40
Purchase #2	$81.76	6.505%	$87.0785	$87.08	$87.10	$87.10
Purchase #3	$31.31	13.310%	$35.4774	$35.48	$35.50	$35.50
Purchase #4	$250.58	5.243%	$263.7179	$263.72	$263.70	$263.70
Purchase #5	$133.55	4.854%	$140.0325	$140.03	$140.05	$140.00
Purchase #6	$119.28	6.707%	$127.2801	$127.28	$127.30	$127.30
Purchase #7	$42.45	6.150%	$45.0607	$45.06	$45.05	$45.10
7 purchase totals =	$814.81		$866.0326	$866.04	$866.10	$866.10