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	$88.82	3.288%	$91.7404	$91.74	$91.75	$91.70
Purchase #2	$113.56	12.359%	$127.5949	$127.59	$127.60	$127.60
Purchase #3	$191.37	4.282%	$199.5645	$199.56	$199.55	$199.60
Purchase #4	$128.87	10.129%	$141.9232	$141.92	$141.90	$141.90
Purchase #5	$13.28	4.799%	$13.9173	$13.92	$13.90	$13.90
Purchase #6	$177.88	3.739%	$184.5309	$184.53	$184.55	$184.50
Purchase #7	$205.75	13.808%	$234.16	$234.16	$234.15	$234.20
7 purchase totals =	$919.53		$993.4312	$993.42	$993.40	$993.40