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	$116.73	5.776%	$123.4723	$123.47	$123.45	$123.50
Purchase #2	$158.53	12.633%	$178.5571	$178.56	$178.55	$178.60
Purchase #3	$57.98	3.756%	$60.1577	$60.16	$60.15	$60.20
Purchase #4	$18.71	4.148%	$19.4861	$19.49	$19.50	$19.50
Purchase #5	$25.28	12.344%	$28.4006	$28.40	$28.40	$28.40
Purchase #6	$178.92	12.217%	$200.7787	$200.78	$200.80	$200.80
Purchase #7	$185.63	12.247%	$208.3641	$208.36	$208.35	$208.40
7 purchase totals =	$741.78		$819.2166	$819.22	$819.20	$819.40