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	$100.69	3.103%	$103.8144	$103.81	$103.80	$103.80
Purchase #2	$50.84	3.663%	$52.7023	$52.70	$52.70	$52.70
Purchase #3	$65.56	4.295%	$68.3758	$68.38	$68.40	$68.40
Purchase #4	$129.82	4.348%	$135.4646	$135.46	$135.45	$135.50
Purchase #5	$54.61	3.468%	$56.5039	$56.50	$56.50	$56.50
Purchase #6	$52.91	12.131%	$59.3285	$59.33	$59.35	$59.30
Purchase #7	$177.74	5.394%	$187.3273	$187.33	$187.35	$187.30
7 purchase totals =	$632.17		$663.5168	$663.51	$663.55	$663.50