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	$40.90	5.560%	$43.174	$43.17	$43.15	$43.20
Purchase #2	$202.78	13.112%	$229.3685	$229.37	$229.35	$229.40
Purchase #3	$115.95	9.856%	$127.378	$127.38	$127.40	$127.40
Purchase #4	$219.87	5.356%	$231.6462	$231.65	$231.65	$231.60
Purchase #5	$7.51	5.637%	$7.9333	$7.93	$7.95	$7.90
Purchase #6	$137.76	13.266%	$156.0352	$156.04	$156.05	$156.00
Purchase #7	$31.28	4.538%	$32.6995	$32.70	$32.70	$32.70
7 purchase totals =	$756.05		$828.2347	$828.24	$828.25	$828.20