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	$40.63	11.725%	$45.3939	$45.39	$45.40	$45.40
Purchase #2	$70.99	10.729%	$78.6065	$78.61	$78.60	$78.60
Purchase #3	$211.32	13.159%	$239.1276	$239.13	$239.15	$239.10
Purchase #4	$62.58	4.206%	$65.2121	$65.21	$65.20	$65.20
Purchase #5	$87.88	12.815%	$99.1418	$99.14	$99.15	$99.10
Purchase #6	$187.95	4.363%	$196.1503	$196.15	$196.15	$196.20
Purchase #7	$55.93	3.424%	$57.845	$57.85	$57.85	$57.80
7 purchase totals =	$717.28		$781.4772	$781.48	$781.50	$781.40