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	$58.60	10.258%	$64.6112	$64.61	$64.60	$64.60
Purchase #2	$47.60	5.115%	$50.0347	$50.03	$50.05	$50.00
Purchase #3	$63.56	12.768%	$71.6753	$71.68	$71.70	$71.70
Purchase #4	$135.84	4.863%	$142.4459	$142.45	$142.45	$142.40
Purchase #5	$116.28	5.777%	$122.9975	$123.00	$123.00	$123.00
Purchase #6	$6.51	12.814%	$7.3442	$7.34	$7.35	$7.30
Purchase #7	$56.65	4.244%	$59.0542	$59.05	$59.05	$59.10
7 purchase totals =	$485.04		$518.1630	$518.16	$518.20	$518.10