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	$132.37	10.437%	$146.1855	$146.19	$146.20	$146.20
Purchase #2	$89.62	6.786%	$95.7016	$95.70	$95.70	$95.70
Purchase #3	$146.36	6.322%	$155.6129	$155.61	$155.60	$155.60
Purchase #4	$7.52	4.209%	$7.8365	$7.84	$7.85	$7.80
Purchase #5	$140.94	4.580%	$147.3951	$147.40	$147.40	$147.40
Purchase #6	$36.41	5.451%	$38.3947	$38.39	$38.40	$38.40
Purchase #7	$71.93	9.510%	$78.7705	$78.77	$78.75	$78.80
7 purchase totals =	$625.15		$669.8968	$669.90	$669.90	$669.90