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	$35.34	6.725%	$37.7166	$37.72	$37.70	$37.70
Purchase #2	$66.62	5.483%	$70.2728	$70.27	$70.25	$70.30
Purchase #3	$149.35	12.757%	$168.4026	$168.40	$168.40	$168.40
Purchase #4	$98.61	12.737%	$111.17	$111.17	$111.15	$111.20
Purchase #5	$151.71	8.336%	$164.3565	$164.36	$164.35	$164.40
Purchase #6	$195.66	12.813%	$220.7299	$220.73	$220.75	$220.70
Purchase #7	$82.89	5.262%	$87.2517	$87.25	$87.25	$87.30
7 purchase totals =	$780.18		$859.9001	$859.90	$859.85	$860.00