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	$143.78	8.480%	$155.9725	$155.97	$155.95	$156.00
Purchase #2	$82.62	9.273%	$90.2814	$90.28	$90.30	$90.30
Purchase #3	$171.95	7.107%	$184.1705	$184.17	$184.15	$184.20
Purchase #4	$34.79	4.524%	$36.3639	$36.36	$36.35	$36.40
Purchase #5	$29.78	9.313%	$32.5534	$32.55	$32.55	$32.60
Purchase #6	$141.99	3.734%	$147.2919	$147.29	$147.30	$147.30
Purchase #7	$18.72	12.363%	$21.0344	$21.03	$21.05	$21.00
7 purchase totals =	$623.63		$667.6680	$667.65	$667.65	$667.80