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	$51.93	9.297%	$56.7579	$56.76	$56.75	$56.80
Purchase #2	$170.67	4.771%	$178.8127	$178.81	$178.80	$178.80
Purchase #3	$242.33	13.301%	$274.5623	$274.56	$274.55	$274.60
Purchase #4	$219.50	6.470%	$233.7017	$233.70	$233.70	$233.70
Purchase #5	$100.75	7.582%	$108.3889	$108.39	$108.40	$108.40
Purchase #6	$96.75	13.541%	$109.8509	$109.85	$109.85	$109.90
Purchase #7	$238.92	12.800%	$269.5018	$269.50	$269.50	$269.50
7 purchase totals =	$1,120.85		$1,231.5762	$1,231.57	$1,231.55	$1,231.70