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	$232.40	7.542%	$249.9276	$249.93	$249.95	$249.90
Purchase #2	$57.95	6.720%	$61.8442	$61.84	$61.85	$61.80
Purchase #3	$79.70	13.817%	$90.7121	$90.71	$90.70	$90.70
Purchase #4	$37.34	13.603%	$42.4194	$42.42	$42.40	$42.40
Purchase #5	$113.27	9.351%	$123.8619	$123.86	$123.85	$123.90
Purchase #6	$111.27	8.486%	$120.7124	$120.71	$120.70	$120.70
Purchase #7	$7.56	8.526%	$8.2046	$8.20	$8.20	$8.20
7 purchase totals =	$639.49		$697.6822	$697.67	$697.65	$697.60