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	$25.59	5.230%	$26.9284	$26.93	$26.95	$26.90
Purchase #2	$103.73	7.402%	$111.4081	$111.41	$111.40	$111.40
Purchase #3	$16.75	7.824%	$18.0605	$18.06	$18.05	$18.10
Purchase #4	$57.73	3.734%	$59.8856	$59.89	$59.90	$59.90
Purchase #5	$89.92	10.732%	$99.5702	$99.57	$99.55	$99.60
Purchase #6	$88.30	4.713%	$92.4616	$92.46	$92.45	$92.50
Purchase #7	$207.80	9.353%	$227.2355	$227.24	$227.25	$227.20
7 purchase totals =	$589.82		$635.5499	$635.56	$635.55	$635.60