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	$60.25	9.743%	$66.1202	$66.12	$66.10	$66.10
Purchase #2	$78.57	8.577%	$85.3089	$85.31	$85.30	$85.30
Purchase #3	$114.52	8.268%	$123.9885	$123.99	$124.00	$124.00
Purchase #4	$99.65	6.166%	$105.7944	$105.79	$105.80	$105.80
Purchase #5	$100.44	8.429%	$108.9061	$108.91	$108.90	$108.90
Purchase #6	$111.61	7.737%	$120.2453	$120.25	$120.25	$120.20
Purchase #7	$135.86	13.669%	$154.4307	$154.43	$154.45	$154.40
7 purchase totals =	$700.90		$764.7941	$764.80	$764.80	$764.70