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	$80.63	12.576%	$90.77	$90.77	$90.75	$90.80
Purchase #2	$7.57	3.314%	$7.8209	$7.82	$7.80	$7.80
Purchase #3	$78.42	4.724%	$82.1246	$82.12	$82.10	$82.10
Purchase #4	$231.89	5.538%	$244.7321	$244.73	$244.75	$244.70
Purchase #5	$53.93	7.788%	$58.1301	$58.13	$58.15	$58.10
Purchase #6	$152.69	10.833%	$169.2309	$169.23	$169.25	$169.20
Purchase #7	$186.69	4.178%	$194.4899	$194.49	$194.50	$194.50
7 purchase totals =	$791.82		$847.2985	$847.29	$847.30	$847.20