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	$38.34	5.146%	$40.313	$40.31	$40.30	$40.30
Purchase #2	$74.60	6.369%	$79.3513	$79.35	$79.35	$79.40
Purchase #3	$41.87	12.820%	$47.2377	$47.24	$47.25	$47.20
Purchase #4	$97.72	7.486%	$105.0353	$105.04	$105.05	$105.00
Purchase #5	$168.89	12.155%	$189.4186	$189.42	$189.40	$189.40
Purchase #6	$71.88	8.671%	$78.1127	$78.11	$78.10	$78.10
Purchase #7	$132.56	3.708%	$137.4753	$137.48	$137.50	$137.50
7 purchase totals =	$625.86		$676.9439	$676.95	$676.95	$676.90