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	$23.61	12.280%	$26.5093	$26.51	$26.50	$26.50
Purchase #2	$179.93	5.727%	$190.2346	$190.23	$190.25	$190.20
Purchase #3	$220.90	6.741%	$235.7909	$235.79	$235.80	$235.80
Purchase #4	$83.78	3.574%	$86.7743	$86.77	$86.75	$86.80
Purchase #5	$245.87	13.626%	$279.3722	$279.37	$279.35	$279.40
Purchase #6	$60.41	9.162%	$65.9448	$65.94	$65.95	$65.90
Purchase #7	$71.89	8.814%	$78.2264	$78.23	$78.25	$78.20
7 purchase totals =	$886.39		$962.8525	$962.84	$962.85	$962.80