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	$28.78	8.725%	$31.2911	$31.29	$31.30	$31.30
Purchase #2	$30.83	9.151%	$33.6513	$33.65	$33.65	$33.70
Purchase #3	$123.53	12.717%	$139.2393	$139.24	$139.25	$139.20
Purchase #4	$86.85	4.705%	$90.9363	$90.94	$90.95	$90.90
Purchase #5	$40.44	5.474%	$42.6537	$42.65	$42.65	$42.70
Purchase #6	$108.70	12.855%	$122.6734	$122.67	$122.65	$122.70
Purchase #7	$130.32	13.164%	$147.4753	$147.48	$147.50	$147.50
7 purchase totals =	$549.45		$607.9204	$607.92	$607.95	$608.00