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	$27.39	3.236%	$28.2763	$28.28	$28.30	$28.30
Purchase #2	$230.60	5.451%	$243.17	$243.17	$243.15	$243.20
Purchase #3	$201.26	3.739%	$208.7851	$208.79	$208.80	$208.80
Purchase #4	$147.71	13.862%	$168.1856	$168.19	$168.20	$168.20
Purchase #5	$249.50	9.843%	$274.0583	$274.06	$274.05	$274.10
Purchase #6	$35.77	13.453%	$40.5821	$40.58	$40.60	$40.60
Purchase #7	$173.27	3.562%	$179.4419	$179.44	$179.45	$179.40
7 purchase totals =	$1,065.50		$1,142.4993	$1,142.51	$1,142.55	$1,142.60