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	$42.51	7.599%	$45.7403	$45.74	$45.75	$45.70
Purchase #2	$233.49	12.708%	$263.1619	$263.16	$263.15	$263.20
Purchase #3	$41.68	6.791%	$44.5105	$44.51	$44.50	$44.50
Purchase #4	$29.40	9.111%	$32.0786	$32.08	$32.10	$32.10
Purchase #5	$50.46	13.393%	$57.2181	$57.22	$57.20	$57.20
Purchase #6	$166.51	11.688%	$185.9717	$185.97	$185.95	$186.00
Purchase #7	$198.43	5.715%	$209.7703	$209.77	$209.75	$209.80
7 purchase totals =	$762.48		$838.4514	$838.45	$838.40	$838.50