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	$46.77	7.378%	$50.2207	$50.22	$50.20	$50.20
Purchase #2	$235.56	7.727%	$253.7617	$253.76	$253.75	$253.80
Purchase #3	$202.77	6.152%	$215.2444	$215.24	$215.25	$215.20
Purchase #4	$233.38	11.773%	$260.8558	$260.86	$260.85	$260.90
Purchase #5	$42.52	11.672%	$47.4829	$47.48	$47.50	$47.50
Purchase #6	$105.81	5.653%	$111.7914	$111.79	$111.80	$111.80
Purchase #7	$162.63	3.575%	$168.444	$168.44	$168.45	$168.40
7 purchase totals =	$1,029.44		$1,107.8009	$1,107.79	$1,107.80	$1,107.80