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	$33.99	9.175%	$37.1086	$37.11	$37.10	$37.10
Purchase #2	$66.93	12.185%	$75.0854	$75.09	$75.10	$75.10
Purchase #3	$27.78	13.725%	$31.5928	$31.59	$31.60	$31.60
Purchase #4	$79.87	13.821%	$90.9088	$90.91	$90.90	$90.90
Purchase #5	$242.61	8.409%	$263.0111	$263.01	$263.00	$263.00
Purchase #6	$38.63	4.194%	$40.2501	$40.25	$40.25	$40.30
Purchase #7	$50.69	13.502%	$57.5342	$57.53	$57.55	$57.50
7 purchase totals =	$540.50		$595.4910	$595.49	$595.50	$595.50