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	$242.86	3.260%	$250.7772	$250.78	$250.80	$250.80
Purchase #2	$67.96	8.732%	$73.8943	$73.89	$73.90	$73.90
Purchase #3	$90.36	9.816%	$99.2297	$99.23	$99.25	$99.20
Purchase #4	$72.33	3.368%	$74.7661	$74.77	$74.75	$74.80
Purchase #5	$111.55	7.745%	$120.1895	$120.19	$120.20	$120.20
Purchase #6	$241.42	12.722%	$272.1335	$272.13	$272.15	$272.10
Purchase #7	$51.35	10.201%	$56.5882	$56.59	$56.60	$56.60
7 purchase totals =	$877.83		$947.5785	$947.58	$947.65	$947.60