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	$170.50	12.839%	$192.3905	$192.39	$192.40	$192.40
Purchase #2	$233.63	5.669%	$246.8745	$246.87	$246.85	$246.90
Purchase #3	$41.56	9.405%	$45.4687	$45.47	$45.45	$45.50
Purchase #4	$250.79	3.109%	$258.5871	$258.59	$258.60	$258.60
Purchase #5	$84.77	3.629%	$87.8463	$87.85	$87.85	$87.80
Purchase #6	$12.91	4.167%	$13.448	$13.45	$13.45	$13.40
Purchase #7	$92.34	8.314%	$100.0171	$100.02	$100.00	$100.00
7 purchase totals =	$886.50		$944.6322	$944.64	$944.60	$944.60