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	$16.64	3.126%	$17.1602	$17.16	$17.15	$17.20
Purchase #2	$199.37	11.429%	$222.156	$222.16	$222.15	$222.20
Purchase #3	$74.82	4.530%	$78.2093	$78.21	$78.20	$78.20
Purchase #4	$136.31	4.411%	$142.3226	$142.32	$142.30	$142.30
Purchase #5	$36.77	10.233%	$40.5327	$40.53	$40.55	$40.50
Purchase #6	$219.89	10.339%	$242.6244	$242.62	$242.60	$242.60
Purchase #7	$70.53	5.424%	$74.3555	$74.36	$74.35	$74.40
7 purchase totals =	$754.33		$817.3607	$817.36	$817.30	$817.40