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	$78.79	5.185%	$82.8753	$82.88	$82.90	$82.90
Purchase #2	$198.38	6.740%	$211.7508	$211.75	$211.75	$211.80
Purchase #3	$139.75	4.414%	$145.9186	$145.92	$145.90	$145.90
Purchase #4	$106.51	6.865%	$113.8219	$113.82	$113.80	$113.80
Purchase #5	$24.58	3.358%	$25.4054	$25.41	$25.40	$25.40
Purchase #6	$87.56	3.303%	$90.4521	$90.45	$90.45	$90.50
Purchase #7	$6.82	8.301%	$7.3861	$7.39	$7.40	$7.40
7 purchase totals =	$642.39		$677.6102	$677.62	$677.60	$677.70