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	$157.26	6.125%	$166.8922	$166.89	$166.90	$166.90
Purchase #2	$133.44	10.439%	$147.3698	$147.37	$147.35	$147.40
Purchase #3	$95.32	11.718%	$106.4896	$106.49	$106.50	$106.50
Purchase #4	$28.92	8.748%	$31.4499	$31.45	$31.45	$31.40
Purchase #5	$52.70	9.839%	$57.8852	$57.89	$57.90	$57.90
Purchase #6	$88.41	12.622%	$99.5691	$99.57	$99.55	$99.60
Purchase #7	$175.87	5.710%	$185.9122	$185.91	$185.90	$185.90
7 purchase totals =	$731.92		$795.5680	$795.57	$795.55	$795.60