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	$116.52	10.361%	$128.5926	$128.59	$128.60	$128.60
Purchase #2	$68.41	5.487%	$72.1637	$72.16	$72.15	$72.20
Purchase #3	$168.74	10.731%	$186.8475	$186.85	$186.85	$186.80
Purchase #4	$212.88	7.567%	$228.9886	$228.99	$229.00	$229.00
Purchase #5	$71.35	12.504%	$80.2716	$80.27	$80.25	$80.30
Purchase #6	$10.37	8.680%	$11.2701	$11.27	$11.25	$11.30
Purchase #7	$37.88	3.763%	$39.3054	$39.31	$39.30	$39.30
7 purchase totals =	$686.15		$747.4395	$747.44	$747.40	$747.50