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	$219.91	10.220%	$242.3848	$242.38	$242.40	$242.40
Purchase #2	$207.69	13.635%	$236.0085	$236.01	$236.00	$236.00
Purchase #3	$94.69	10.162%	$104.3124	$104.31	$104.30	$104.30
Purchase #4	$144.31	5.641%	$152.4505	$152.45	$152.45	$152.50
Purchase #5	$39.41	5.320%	$41.5066	$41.51	$41.50	$41.50
Purchase #6	$92.77	7.220%	$99.468	$99.47	$99.45	$99.50
Purchase #7	$92.50	7.192%	$99.1526	$99.15	$99.15	$99.20
7 purchase totals =	$891.28		$975.2834	$975.28	$975.25	$975.40