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	$153.96	11.596%	$171.8132	$171.81	$171.80	$171.80
Purchase #2	$248.66	8.401%	$269.5499	$269.55	$269.55	$269.50
Purchase #3	$40.36	7.511%	$43.3914	$43.39	$43.40	$43.40
Purchase #4	$76.98	6.632%	$82.0853	$82.09	$82.10	$82.10
Purchase #5	$172.61	3.412%	$178.4995	$178.50	$178.50	$178.50
Purchase #6	$71.86	13.275%	$81.3994	$81.40	$81.40	$81.40
Purchase #7	$241.90	7.799%	$260.7658	$260.77	$260.75	$260.80
7 purchase totals =	$1,006.33		$1,087.5045	$1,087.51	$1,087.50	$1,087.50