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	$242.39	13.547%	$275.2266	$275.23	$275.25	$275.20
Purchase #2	$107.86	8.775%	$117.3247	$117.32	$117.30	$117.30
Purchase #3	$37.79	6.531%	$40.2581	$40.26	$40.25	$40.30
Purchase #4	$34.61	5.466%	$36.5018	$36.50	$36.50	$36.50
Purchase #5	$28.63	12.707%	$32.268	$32.27	$32.25	$32.30
Purchase #6	$108.73	7.319%	$116.6879	$116.69	$116.70	$116.70
Purchase #7	$192.53	13.393%	$218.3155	$218.32	$218.30	$218.30
7 purchase totals =	$752.54		$836.5826	$836.59	$836.55	$836.60