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	$37.42	6.304%	$39.779	$39.78	$39.80	$39.80
Purchase #2	$76.98	10.838%	$85.3231	$85.32	$85.30	$85.30
Purchase #3	$196.42	11.299%	$218.6135	$218.61	$218.60	$218.60
Purchase #4	$97.83	12.759%	$110.3121	$110.31	$110.30	$110.30
Purchase #5	$133.47	5.225%	$140.4438	$140.44	$140.45	$140.40
Purchase #6	$128.31	7.439%	$137.855	$137.86	$137.85	$137.90
Purchase #7	$238.65	8.693%	$259.3958	$259.40	$259.40	$259.40
7 purchase totals =	$909.08		$991.7223	$991.72	$991.70	$991.70