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	$58.48	11.864%	$65.4181	$65.42	$65.40	$65.40
Purchase #2	$141.41	6.254%	$150.2538	$150.25	$150.25	$150.30
Purchase #3	$60.58	10.562%	$66.9785	$66.98	$67.00	$67.00
Purchase #4	$46.80	11.793%	$52.3191	$52.32	$52.30	$52.30
Purchase #5	$120.57	13.676%	$137.0592	$137.06	$137.05	$137.10
Purchase #6	$229.65	11.672%	$256.4547	$256.45	$256.45	$256.50
Purchase #7	$116.51	10.833%	$129.1315	$129.13	$129.15	$129.10
7 purchase totals =	$774.00		$857.6149	$857.61	$857.60	$857.70