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	$42.49	6.361%	$45.1928	$45.19	$45.20	$45.20
Purchase #2	$153.70	10.522%	$169.8723	$169.87	$169.85	$169.90
Purchase #3	$37.80	11.857%	$42.2819	$42.28	$42.30	$42.30
Purchase #4	$121.86	13.706%	$138.5621	$138.56	$138.55	$138.60
Purchase #5	$156.30	6.170%	$165.9437	$165.94	$165.95	$165.90
Purchase #6	$24.49	12.130%	$27.4606	$27.46	$27.45	$27.50
Purchase #7	$72.37	10.748%	$80.1483	$80.15	$80.15	$80.10
7 purchase totals =	$609.01		$669.4617	$669.45	$669.45	$669.50