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	$132.36	3.339%	$136.7795	$136.78	$136.80	$136.80
Purchase #2	$85.27	6.590%	$90.8893	$90.89	$90.90	$90.90
Purchase #3	$98.26	8.348%	$106.4627	$106.46	$106.45	$106.50
Purchase #4	$239.98	6.365%	$255.2547	$255.25	$255.25	$255.30
Purchase #5	$191.62	8.463%	$207.8368	$207.84	$207.85	$207.80
Purchase #6	$142.89	5.756%	$151.1147	$151.11	$151.10	$151.10
Purchase #7	$132.57	8.145%	$143.3678	$143.37	$143.35	$143.40
7 purchase totals =	$1,022.95		$1,091.7055	$1,091.70	$1,091.70	$1,091.80