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	$83.85	7.158%	$89.852	$89.85	$89.85	$89.90
Purchase #2	$33.53	10.170%	$36.94	$36.94	$36.95	$36.90
Purchase #3	$66.63	3.782%	$69.1499	$69.15	$69.15	$69.10
Purchase #4	$78.88	13.747%	$89.7236	$89.72	$89.70	$89.70
Purchase #5	$93.28	13.687%	$106.0472	$106.05	$106.05	$106.00
Purchase #6	$12.36	10.621%	$13.6728	$13.67	$13.65	$13.70
Purchase #7	$143.52	12.548%	$161.5289	$161.53	$161.55	$161.50
7 purchase totals =	$512.05		$566.9144	$566.91	$566.90	$566.80