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	$142.71	3.302%	$147.4223	$147.42	$147.40	$147.40
Purchase #2	$88.54	10.728%	$98.0386	$98.04	$98.05	$98.00
Purchase #3	$215.78	4.685%	$225.8893	$225.89	$225.90	$225.90
Purchase #4	$53.51	3.172%	$55.2073	$55.21	$55.20	$55.20
Purchase #5	$43.96	12.699%	$49.5425	$49.54	$49.55	$49.50
Purchase #6	$57.81	6.516%	$61.5769	$61.58	$61.60	$61.60
Purchase #7	$29.45	6.168%	$31.2665	$31.27	$31.25	$31.30
7 purchase totals =	$631.76		$668.9434	$668.95	$668.95	$668.90