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	$50.51	13.413%	$57.2849	$57.28	$57.30	$57.30
Purchase #2	$151.79	6.617%	$161.8339	$161.83	$161.85	$161.80
Purchase #3	$75.86	8.718%	$82.4735	$82.47	$82.45	$82.50
Purchase #4	$243.92	12.867%	$275.3052	$275.31	$275.30	$275.30
Purchase #5	$64.51	11.250%	$71.7674	$71.77	$71.75	$71.80
Purchase #6	$224.35	8.524%	$243.4736	$243.47	$243.45	$243.50
Purchase #7	$176.58	10.295%	$194.7589	$194.76	$194.75	$194.80
7 purchase totals =	$987.52		$1,086.8974	$1,086.89	$1,086.85	$1,087.00