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	$137.35	13.402%	$155.7576	$155.76	$155.75	$155.80
Purchase #2	$170.54	12.634%	$192.086	$192.09	$192.10	$192.10
Purchase #3	$80.60	13.486%	$91.4697	$91.47	$91.45	$91.50
Purchase #4	$27.56	13.740%	$31.3467	$31.35	$31.35	$31.30
Purchase #5	$100.34	7.737%	$108.1033	$108.10	$108.10	$108.10
Purchase #6	$118.44	4.591%	$123.8776	$123.88	$123.90	$123.90
Purchase #7	$54.68	10.557%	$60.4526	$60.45	$60.45	$60.50
7 purchase totals =	$689.51		$763.0935	$763.10	$763.10	$763.20