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	$84.85	5.695%	$89.6822	$89.68	$89.70	$89.70
Purchase #2	$233.59	11.211%	$259.7778	$259.78	$259.80	$259.80
Purchase #3	$19.53	8.700%	$21.2291	$21.23	$21.25	$21.20
Purchase #4	$69.96	11.759%	$78.1866	$78.19	$78.20	$78.20
Purchase #5	$5.25	13.218%	$5.9439	$5.94	$5.95	$5.90
Purchase #6	$184.60	4.362%	$192.6523	$192.65	$192.65	$192.70
Purchase #7	$140.40	10.296%	$154.8556	$154.86	$154.85	$154.90
7 purchase totals =	$738.18		$802.3275	$802.33	$802.40	$802.40