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	$220.80	13.285%	$250.1333	$250.13	$250.15	$250.10
Purchase #2	$30.86	6.171%	$32.7644	$32.76	$32.75	$32.80
Purchase #3	$232.45	11.322%	$258.768	$258.77	$258.75	$258.80
Purchase #4	$180.60	3.439%	$186.8108	$186.81	$186.80	$186.80
Purchase #5	$67.65	5.632%	$71.46	$71.46	$71.45	$71.50
Purchase #6	$167.83	13.106%	$189.8258	$189.83	$189.85	$189.80
Purchase #7	$204.40	11.552%	$228.0123	$228.01	$228.00	$228.00
7 purchase totals =	$1,104.59		$1,217.7746	$1,217.77	$1,217.75	$1,217.80