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	$65.74	9.174%	$71.771	$71.77	$71.75	$71.80
Purchase #2	$129.35	8.708%	$140.6138	$140.61	$140.60	$140.60
Purchase #3	$126.53	9.640%	$138.7275	$138.73	$138.75	$138.70
Purchase #4	$86.27	4.401%	$90.0667	$90.07	$90.05	$90.10
Purchase #5	$167.54	12.268%	$188.0938	$188.09	$188.10	$188.10
Purchase #6	$32.41	4.191%	$33.7683	$33.77	$33.75	$33.80
Purchase #7	$130.89	11.372%	$145.7748	$145.77	$145.75	$145.80
7 purchase totals =	$738.73		$808.8159	$808.81	$808.75	$808.90