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	$59.95	3.865%	$62.2671	$62.27	$62.25	$62.30
Purchase #2	$84.54	6.205%	$89.7857	$89.79	$89.80	$89.80
Purchase #3	$100.36	10.807%	$111.2059	$111.21	$111.20	$111.20
Purchase #4	$129.58	7.731%	$139.5978	$139.60	$139.60	$139.60
Purchase #5	$71.46	12.212%	$80.1867	$80.19	$80.20	$80.20
Purchase #6	$200.34	5.333%	$211.0241	$211.02	$211.00	$211.00
Purchase #7	$146.89	3.407%	$151.8945	$151.89	$151.90	$151.90
7 purchase totals =	$793.12		$845.9618	$845.97	$845.95	$846.00