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	$244.44	10.425%	$269.9229	$269.92	$269.90	$269.90
Purchase #2	$233.80	12.764%	$263.6422	$263.64	$263.65	$263.60
Purchase #3	$175.29	5.842%	$185.5304	$185.53	$185.55	$185.50
Purchase #4	$122.45	4.795%	$128.3215	$128.32	$128.30	$128.30
Purchase #5	$241.80	11.266%	$269.0412	$269.04	$269.05	$269.00
Purchase #6	$16.61	10.808%	$18.4052	$18.41	$18.40	$18.40
Purchase #7	$55.47	13.172%	$62.7765	$62.78	$62.80	$62.80
7 purchase totals =	$1,089.86		$1,197.6399	$1,197.64	$1,197.65	$1,197.50