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	$79.87	12.568%	$89.9081	$89.91	$89.90	$89.90
Purchase #2	$36.46	4.129%	$37.9654	$37.97	$37.95	$38.00
Purchase #3	$242.75	4.408%	$253.4504	$253.45	$253.45	$253.50
Purchase #4	$88.40	12.677%	$99.6065	$99.61	$99.60	$99.60
Purchase #5	$88.79	8.225%	$96.093	$96.09	$96.10	$96.10
Purchase #6	$64.91	9.675%	$71.19	$71.19	$71.20	$71.20
Purchase #7	$41.66	6.531%	$44.3808	$44.38	$44.40	$44.40
7 purchase totals =	$642.84		$692.5942	$692.60	$692.60	$692.70