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	$46.25	8.844%	$50.3404	$50.34	$50.35	$50.30
Purchase #2	$87.85	9.178%	$95.9129	$95.91	$95.90	$95.90
Purchase #3	$24.36	4.769%	$25.5217	$25.52	$25.50	$25.50
Purchase #4	$90.35	4.205%	$94.1492	$94.15	$94.15	$94.10
Purchase #5	$152.61	13.272%	$172.8644	$172.86	$172.85	$172.90
Purchase #6	$165.73	7.487%	$178.1382	$178.14	$178.15	$178.10
Purchase #7	$70.67	3.567%	$73.1908	$73.19	$73.20	$73.20
7 purchase totals =	$637.82		$690.1176	$690.11	$690.10	$690.00