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	$196.27	5.155%	$206.3877	$206.39	$206.40	$206.40
Purchase #2	$204.55	11.786%	$228.6583	$228.66	$228.65	$228.70
Purchase #3	$22.83	13.248%	$25.8545	$25.85	$25.85	$25.90
Purchase #4	$140.86	12.376%	$158.2928	$158.29	$158.30	$158.30
Purchase #5	$35.31	7.628%	$38.0034	$38.00	$38.00	$38.00
Purchase #6	$196.96	13.518%	$223.5851	$223.59	$223.60	$223.60
Purchase #7	$44.96	6.470%	$47.8689	$47.87	$47.85	$47.90
7 purchase totals =	$841.74		$928.6507	$928.65	$928.65	$928.80