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	$29.84	5.304%	$31.4227	$31.42	$31.40	$31.40
Purchase #2	$134.29	7.268%	$144.0502	$144.05	$144.05	$144.10
Purchase #3	$231.40	6.158%	$245.6496	$245.65	$245.65	$245.60
Purchase #4	$108.89	13.705%	$123.8134	$123.81	$123.80	$123.80
Purchase #5	$158.31	13.174%	$179.1658	$179.17	$179.15	$179.20
Purchase #6	$231.30	7.310%	$248.208	$248.21	$248.20	$248.20
Purchase #7	$209.74	8.796%	$228.1887	$228.19	$228.20	$228.20
7 purchase totals =	$1,103.77		$1,200.4984	$1,200.50	$1,200.45	$1,200.50