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	$168.36	7.146%	$180.391	$180.39	$180.40	$180.40
Purchase #2	$211.92	5.296%	$223.1433	$223.14	$223.15	$223.10
Purchase #3	$113.95	7.552%	$122.5555	$122.56	$122.55	$122.60
Purchase #4	$83.59	8.231%	$90.4703	$90.47	$90.45	$90.50
Purchase #5	$65.83	7.428%	$70.7199	$70.72	$70.70	$70.70
Purchase #6	$103.67	6.117%	$110.0115	$110.01	$110.00	$110.00
Purchase #7	$29.61	13.287%	$33.5443	$33.54	$33.55	$33.50
7 purchase totals =	$776.93		$830.8358	$830.83	$830.80	$830.80