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	$199.91	10.616%	$221.1324	$221.13	$221.15	$221.10
Purchase #2	$54.42	12.120%	$61.0157	$61.02	$61.00	$61.00
Purchase #3	$200.67	11.227%	$223.1992	$223.20	$223.20	$223.20
Purchase #4	$155.93	8.761%	$169.591	$169.59	$169.60	$169.60
Purchase #5	$127.62	13.151%	$144.4033	$144.40	$144.40	$144.40
Purchase #6	$96.54	9.159%	$105.3821	$105.38	$105.40	$105.40
Purchase #7	$16.51	6.155%	$17.5262	$17.53	$17.55	$17.50
7 purchase totals =	$851.60		$942.2499	$942.25	$942.30	$942.20