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	$9.60	5.477%	$10.1258	$10.13	$10.15	$10.10
Purchase #2	$69.28	3.769%	$71.8912	$71.89	$71.90	$71.90
Purchase #3	$84.27	5.853%	$89.2023	$89.20	$89.20	$89.20
Purchase #4	$23.40	7.621%	$25.1833	$25.18	$25.20	$25.20
Purchase #5	$186.59	10.321%	$205.848	$205.85	$205.85	$205.80
Purchase #6	$53.89	12.386%	$60.5648	$60.56	$60.55	$60.60
Purchase #7	$47.86	5.543%	$50.5129	$50.51	$50.50	$50.50
7 purchase totals =	$474.89		$513.3283	$513.32	$513.35	$513.30