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	$28.30	10.615%	$31.304	$31.30	$31.30	$31.30
Purchase #2	$222.71	3.353%	$230.1775	$230.18	$230.20	$230.20
Purchase #3	$96.59	9.233%	$105.5082	$105.51	$105.50	$105.50
Purchase #4	$149.90	12.673%	$168.8968	$168.90	$168.90	$168.90
Purchase #5	$180.38	6.209%	$191.5798	$191.58	$191.60	$191.60
Purchase #6	$185.72	4.378%	$193.8508	$193.85	$193.85	$193.90
Purchase #7	$167.77	6.701%	$179.0123	$179.01	$179.00	$179.00
7 purchase totals =	$1,031.37		$1,100.3294	$1,100.33	$1,100.35	$1,100.40