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	$71.84	7.343%	$77.1152	$77.12	$77.10	$77.10
Purchase #2	$69.39	3.250%	$71.6452	$71.65	$71.65	$71.60
Purchase #3	$78.65	11.371%	$87.5933	$87.59	$87.60	$87.60
Purchase #4	$111.88	7.483%	$120.252	$120.25	$120.25	$120.30
Purchase #5	$154.80	12.104%	$173.537	$173.54	$173.55	$173.50
Purchase #6	$99.70	5.227%	$104.9113	$104.91	$104.90	$104.90
Purchase #7	$184.79	8.373%	$200.2625	$200.26	$200.25	$200.30
7 purchase totals =	$771.05		$835.3165	$835.32	$835.30	$835.30