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	$38.72	11.363%	$43.1198	$43.12	$43.10	$43.10
Purchase #2	$91.38	13.105%	$103.3553	$103.36	$103.35	$103.40
Purchase #3	$246.85	8.798%	$268.5679	$268.57	$268.55	$268.60
Purchase #4	$22.43	8.311%	$24.2942	$24.29	$24.30	$24.30
Purchase #5	$196.63	10.490%	$217.2565	$217.26	$217.25	$217.30
Purchase #6	$65.45	10.434%	$72.2791	$72.28	$72.30	$72.30
Purchase #7	$66.75	5.431%	$70.3752	$70.38	$70.40	$70.40
7 purchase totals =	$728.21		$799.2480	$799.26	$799.25	$799.40