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	$33.90	7.572%	$36.4669	$36.47	$36.45	$36.50
Purchase #2	$60.26	8.816%	$65.5725	$65.57	$65.55	$65.60
Purchase #3	$37.62	13.220%	$42.5934	$42.59	$42.60	$42.60
Purchase #4	$242.99	13.391%	$275.5288	$275.53	$275.55	$275.50
Purchase #5	$89.73	6.297%	$95.3803	$95.38	$95.40	$95.40
Purchase #6	$172.91	4.542%	$180.7636	$180.76	$180.75	$180.80
Purchase #7	$143.48	10.781%	$158.9486	$158.95	$158.95	$158.90
7 purchase totals =	$780.89		$855.2541	$855.25	$855.25	$855.30