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	$82.90	9.162%	$90.4953	$90.50	$90.50	$90.50
Purchase #2	$27.80	6.485%	$29.6028	$29.60	$29.60	$29.60
Purchase #3	$156.84	5.347%	$165.2262	$165.23	$165.25	$165.20
Purchase #4	$92.89	7.274%	$99.6468	$99.65	$99.65	$99.60
Purchase #5	$157.29	6.382%	$167.3282	$167.33	$167.35	$167.30
Purchase #6	$228.94	4.674%	$239.6407	$239.64	$239.65	$239.60
Purchase #7	$139.96	5.150%	$147.1679	$147.17	$147.15	$147.20
7 purchase totals =	$886.62		$939.1079	$939.12	$939.15	$939.00