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	$125.50	12.348%	$140.9967	$141.00	$141.00	$141.00
Purchase #2	$153.75	9.753%	$168.7452	$168.75	$168.75	$168.70
Purchase #3	$28.55	4.437%	$29.8168	$29.82	$29.80	$29.80
Purchase #4	$65.88	10.675%	$72.9127	$72.91	$72.90	$72.90
Purchase #5	$98.35	5.221%	$103.4849	$103.48	$103.50	$103.50
Purchase #6	$47.64	13.643%	$54.1395	$54.14	$54.15	$54.10
Purchase #7	$116.97	5.422%	$123.3121	$123.31	$123.30	$123.30
7 purchase totals =	$636.64		$693.4079	$693.41	$693.40	$693.30