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	$200.90	10.696%	$222.3883	$222.39	$222.40	$222.40
Purchase #2	$65.92	8.789%	$71.7137	$71.71	$71.70	$71.70
Purchase #3	$145.28	10.287%	$160.225	$160.23	$160.25	$160.20
Purchase #4	$78.63	11.136%	$87.3862	$87.39	$87.40	$87.40
Purchase #5	$56.64	12.419%	$63.6741	$63.67	$63.65	$63.70
Purchase #6	$63.89	4.238%	$66.5977	$66.60	$66.60	$66.60
Purchase #7	$62.37	8.695%	$67.7931	$67.79	$67.80	$67.80
7 purchase totals =	$673.63		$739.7781	$739.78	$739.80	$739.80