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	$240.76	11.685%	$268.8928	$268.89	$268.90	$268.90
Purchase #2	$58.30	11.847%	$65.2068	$65.21	$65.20	$65.20
Purchase #3	$189.29	5.804%	$200.2764	$200.28	$200.30	$200.30
Purchase #4	$40.65	4.426%	$42.4492	$42.45	$42.45	$42.40
Purchase #5	$178.79	6.703%	$190.7743	$190.77	$190.75	$190.80
Purchase #6	$177.37	4.637%	$185.5946	$185.59	$185.60	$185.60
Purchase #7	$101.50	7.340%	$108.9501	$108.95	$108.95	$109.00
7 purchase totals =	$986.66		$1,062.1442	$1,062.14	$1,062.15	$1,062.20