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	$243.56	5.450%	$256.834	$256.83	$256.85	$256.80
Purchase #2	$21.52	13.309%	$24.3841	$24.38	$24.40	$24.40
Purchase #3	$139.25	13.627%	$158.2256	$158.23	$158.25	$158.20
Purchase #4	$30.62	7.180%	$32.8185	$32.82	$32.80	$32.80
Purchase #5	$250.30	7.297%	$268.5644	$268.56	$268.55	$268.60
Purchase #6	$31.89	13.451%	$36.1795	$36.18	$36.20	$36.20
Purchase #7	$22.37	13.566%	$25.4047	$25.40	$25.40	$25.40
7 purchase totals =	$739.51		$802.4108	$802.40	$802.45	$802.40