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	$48.69	6.583%	$51.8953	$51.90	$51.90	$51.90
Purchase #2	$88.29	9.656%	$96.8153	$96.82	$96.80	$96.80
Purchase #3	$101.93	9.823%	$111.9426	$111.94	$111.95	$111.90
Purchase #4	$150.54	13.308%	$170.5739	$170.57	$170.55	$170.60
Purchase #5	$195.49	13.777%	$222.4227	$222.42	$222.40	$222.40
Purchase #6	$33.77	9.318%	$36.9167	$36.92	$36.90	$36.90
Purchase #7	$109.86	6.510%	$117.0119	$117.01	$117.00	$117.00
7 purchase totals =	$728.57		$807.5784	$807.58	$807.50	$807.50