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	$176.48	7.731%	$190.1237	$190.12	$190.10	$190.10
Purchase #2	$38.50	5.492%	$40.6144	$40.61	$40.60	$40.60
Purchase #3	$38.76	4.525%	$40.5139	$40.51	$40.50	$40.50
Purchase #4	$165.39	12.394%	$185.8884	$185.89	$185.90	$185.90
Purchase #5	$49.32	9.549%	$54.0296	$54.03	$54.05	$54.00
Purchase #6	$90.86	8.725%	$98.7875	$98.79	$98.80	$98.80
Purchase #7	$28.63	5.851%	$30.3051	$30.31	$30.30	$30.30
7 purchase totals =	$587.94		$640.2626	$640.26	$640.25	$640.20