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	$37.90	6.363%	$40.3116	$40.31	$40.30	$40.30
Purchase #2	$159.54	11.421%	$177.7611	$177.76	$177.75	$177.80
Purchase #3	$227.42	12.795%	$256.5184	$256.52	$256.50	$256.50
Purchase #4	$83.43	3.581%	$86.4176	$86.42	$86.40	$86.40
Purchase #5	$110.54	11.800%	$123.5837	$123.58	$123.60	$123.60
Purchase #6	$177.97	10.638%	$196.9024	$196.90	$196.90	$196.90
Purchase #7	$123.34	10.319%	$136.0675	$136.07	$136.05	$136.10
7 purchase totals =	$920.14		$1,017.5623	$1,017.56	$1,017.50	$1,017.60