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	$52.30	7.467%	$56.2052	$56.21	$56.20	$56.20
Purchase #2	$94.39	5.265%	$99.3596	$99.36	$99.35	$99.40
Purchase #3	$241.74	5.116%	$254.1074	$254.11	$254.10	$254.10
Purchase #4	$233.83	6.686%	$249.4639	$249.46	$249.45	$249.50
Purchase #5	$92.40	8.599%	$100.3455	$100.35	$100.35	$100.30
Purchase #6	$238.27	7.410%	$255.9258	$255.93	$255.95	$255.90
Purchase #7	$247.62	11.209%	$275.3757	$275.38	$275.40	$275.40
7 purchase totals =	$1,200.55		$1,290.7831	$1,290.80	$1,290.80	$1,290.80