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	$48.59	3.614%	$50.346	$50.35	$50.35	$50.30
Purchase #2	$32.28	3.487%	$33.4056	$33.41	$33.40	$33.40
Purchase #3	$38.39	13.182%	$43.4506	$43.45	$43.45	$43.50
Purchase #4	$77.26	10.872%	$85.6597	$85.66	$85.65	$85.70
Purchase #5	$85.39	5.810%	$90.3512	$90.35	$90.35	$90.40
Purchase #6	$189.25	6.571%	$201.6856	$201.69	$201.70	$201.70
Purchase #7	$140.84	6.550%	$150.065	$150.07	$150.05	$150.10
7 purchase totals =	$612.00		$654.9637	$654.98	$654.95	$655.10