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	$219.77	13.490%	$249.417	$249.42	$249.40	$249.40
Purchase #2	$113.92	8.174%	$123.2318	$123.23	$123.25	$123.20
Purchase #3	$115.38	6.607%	$123.0032	$123.00	$123.00	$123.00
Purchase #4	$69.72	13.506%	$79.1364	$79.14	$79.15	$79.10
Purchase #5	$74.94	5.224%	$78.8549	$78.85	$78.85	$78.90
Purchase #6	$10.80	12.807%	$12.1832	$12.18	$12.20	$12.20
Purchase #7	$33.68	13.243%	$38.1402	$38.14	$38.15	$38.10
7 purchase totals =	$638.21		$703.9667	$703.96	$704.00	$703.90