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	$9.94	8.786%	$10.8133	$10.81	$10.80	$10.80
Purchase #2	$89.79	11.233%	$99.8761	$99.88	$99.90	$99.90
Purchase #3	$203.69	6.645%	$217.2252	$217.23	$217.25	$217.20
Purchase #4	$243.89	3.337%	$252.0286	$252.03	$252.05	$252.00
Purchase #5	$184.75	6.440%	$196.6479	$196.65	$196.65	$196.60
Purchase #6	$144.76	12.456%	$162.7913	$162.79	$162.80	$162.80
Purchase #7	$53.54	6.330%	$56.9291	$56.93	$56.95	$56.90
7 purchase totals =	$930.36		$996.3115	$996.32	$996.40	$996.20