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	$50.52	6.504%	$53.8058	$53.81	$53.80	$53.80
Purchase #2	$32.80	13.566%	$37.2496	$37.25	$37.25	$37.20
Purchase #3	$244.68	10.104%	$269.4025	$269.40	$269.40	$269.40
Purchase #4	$50.76	9.218%	$55.4391	$55.44	$55.45	$55.40
Purchase #5	$199.26	10.267%	$219.718	$219.72	$219.70	$219.70
Purchase #6	$209.92	5.232%	$220.903	$220.90	$220.90	$220.90
Purchase #7	$92.60	8.556%	$100.5229	$100.52	$100.50	$100.50
7 purchase totals =	$880.54		$957.0409	$957.04	$957.00	$956.90