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	$242.47	13.705%	$275.7005	$275.70	$275.70	$275.70
Purchase #2	$92.36	7.792%	$99.5567	$99.56	$99.55	$99.60
Purchase #3	$108.28	12.496%	$121.8107	$121.81	$121.80	$121.80
Purchase #4	$143.53	4.710%	$150.2903	$150.29	$150.30	$150.30
Purchase #5	$240.75	13.382%	$272.9672	$272.97	$272.95	$273.00
Purchase #6	$47.56	6.151%	$50.4854	$50.49	$50.50	$50.50
Purchase #7	$113.59	12.221%	$127.4718	$127.47	$127.45	$127.50
7 purchase totals =	$988.54		$1,098.2826	$1,098.29	$1,098.25	$1,098.40