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	$42.69	7.399%	$45.8486	$45.85	$45.85	$45.80
Purchase #2	$76.49	13.103%	$86.5125	$86.51	$86.50	$86.50
Purchase #3	$108.62	8.386%	$117.7289	$117.73	$117.75	$117.70
Purchase #4	$171.41	6.679%	$182.8585	$182.86	$182.85	$182.90
Purchase #5	$194.87	8.502%	$211.4378	$211.44	$211.45	$211.40
Purchase #6	$78.51	10.296%	$86.5934	$86.59	$86.60	$86.60
Purchase #7	$188.75	13.678%	$214.5672	$214.57	$214.55	$214.60
7 purchase totals =	$861.34		$945.5469	$945.55	$945.55	$945.50