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	$126.47	4.279%	$131.8817	$131.88	$131.90	$131.90
Purchase #2	$95.38	6.520%	$101.5988	$101.60	$101.60	$101.60
Purchase #3	$199.91	5.729%	$211.3628	$211.36	$211.35	$211.40
Purchase #4	$19.31	10.386%	$21.3155	$21.32	$21.30	$21.30
Purchase #5	$73.96	11.259%	$82.2872	$82.29	$82.30	$82.30
Purchase #6	$217.50	6.111%	$230.7914	$230.79	$230.80	$230.80
Purchase #7	$9.92	3.413%	$10.2586	$10.26	$10.25	$10.30
7 purchase totals =	$742.45		$789.4960	$789.50	$789.50	$789.60