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	$191.79	11.692%	$214.2141	$214.21	$214.20	$214.20
Purchase #2	$146.43	7.142%	$156.888	$156.89	$156.90	$156.90
Purchase #3	$197.40	8.684%	$214.5422	$214.54	$214.55	$214.50
Purchase #4	$81.64	8.776%	$88.8047	$88.80	$88.80	$88.80
Purchase #5	$72.70	8.459%	$78.8497	$78.85	$78.85	$78.80
Purchase #6	$64.56	11.284%	$71.845	$71.85	$71.85	$71.80
Purchase #7	$11.81	7.820%	$12.7335	$12.73	$12.75	$12.70
7 purchase totals =	$766.33		$837.8772	$837.87	$837.90	$837.70