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	$40.48	8.510%	$43.9248	$43.92	$43.90	$43.90
Purchase #2	$162.52	7.873%	$175.3152	$175.32	$175.30	$175.30
Purchase #3	$217.27	8.504%	$235.7466	$235.75	$235.75	$235.70
Purchase #4	$64.82	10.254%	$71.4666	$71.47	$71.45	$71.50
Purchase #5	$13.53	13.542%	$15.3622	$15.36	$15.35	$15.40
Purchase #6	$82.41	10.267%	$90.871	$90.87	$90.85	$90.90
Purchase #7	$145.45	7.144%	$155.8409	$155.84	$155.85	$155.80
7 purchase totals =	$726.48		$788.5273	$788.53	$788.45	$788.50