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	$66.65	7.140%	$71.4088	$71.41	$71.40	$71.40
Purchase #2	$212.61	3.657%	$220.3851	$220.39	$220.40	$220.40
Purchase #3	$229.68	12.731%	$258.9206	$258.92	$258.90	$258.90
Purchase #4	$38.57	4.131%	$40.1633	$40.16	$40.15	$40.20
Purchase #5	$77.67	7.285%	$83.3283	$83.33	$83.35	$83.30
Purchase #6	$46.37	12.787%	$52.2993	$52.30	$52.30	$52.30
Purchase #7	$232.35	4.195%	$242.0971	$242.10	$242.10	$242.10
7 purchase totals =	$903.90		$968.6025	$968.61	$968.60	$968.60