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	$59.56	12.271%	$66.8686	$66.87	$66.85	$66.90
Purchase #2	$215.91	10.811%	$239.252	$239.25	$239.25	$239.30
Purchase #3	$75.77	9.734%	$83.1455	$83.15	$83.15	$83.10
Purchase #4	$75.79	12.520%	$85.2789	$85.28	$85.30	$85.30
Purchase #5	$19.38	7.521%	$20.8376	$20.84	$20.85	$20.80
Purchase #6	$65.75	3.261%	$67.8941	$67.89	$67.90	$67.90
Purchase #7	$149.54	6.477%	$159.2257	$159.23	$159.25	$159.20
7 purchase totals =	$661.70		$722.5024	$722.51	$722.55	$722.50