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	$83.57	6.675%	$89.1483	$89.15	$89.15	$89.10
Purchase #2	$115.32	7.626%	$124.1143	$124.11	$124.10	$124.10
Purchase #3	$11.47	10.429%	$12.6662	$12.67	$12.65	$12.70
Purchase #4	$134.26	8.471%	$145.6332	$145.63	$145.65	$145.60
Purchase #5	$156.56	9.843%	$171.9702	$171.97	$171.95	$172.00
Purchase #6	$128.94	12.156%	$144.6139	$144.61	$144.60	$144.60
Purchase #7	$187.36	11.260%	$208.4567	$208.46	$208.45	$208.50
7 purchase totals =	$817.48		$896.6028	$896.60	$896.55	$896.60