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	$181.41	12.108%	$203.3751	$203.38	$203.40	$203.40
Purchase #2	$242.67	6.396%	$258.1912	$258.19	$258.20	$258.20
Purchase #3	$230.59	6.517%	$245.6176	$245.62	$245.60	$245.60
Purchase #4	$53.77	10.147%	$59.226	$59.23	$59.25	$59.20
Purchase #5	$134.86	7.119%	$144.4607	$144.46	$144.45	$144.50
Purchase #6	$44.76	3.845%	$46.481	$46.48	$46.50	$46.50
Purchase #7	$31.62	13.288%	$35.8217	$35.82	$35.80	$35.80
7 purchase totals =	$919.68		$993.1733	$993.18	$993.20	$993.20