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	$152.29	9.529%	$166.8017	$166.80	$166.80	$166.80
Purchase #2	$249.90	9.211%	$272.9183	$272.92	$272.90	$272.90
Purchase #3	$127.59	8.757%	$138.7631	$138.76	$138.75	$138.80
Purchase #4	$162.29	6.721%	$173.1975	$173.20	$173.20	$173.20
Purchase #5	$75.65	4.168%	$78.8031	$78.80	$78.80	$78.80
Purchase #6	$25.54	11.155%	$28.389	$28.39	$28.40	$28.40
Purchase #7	$223.53	13.579%	$253.8831	$253.88	$253.90	$253.90
7 purchase totals =	$1,016.79		$1,112.7558	$1,112.75	$1,112.75	$1,112.80