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	$38.47	6.140%	$40.8321	$40.83	$40.85	$40.80
Purchase #2	$31.98	5.855%	$33.8524	$33.85	$33.85	$33.90
Purchase #3	$206.65	8.651%	$224.5273	$224.53	$224.55	$224.50
Purchase #4	$43.94	4.480%	$45.9085	$45.91	$45.90	$45.90
Purchase #5	$85.53	12.683%	$96.3778	$96.38	$96.40	$96.40
Purchase #6	$71.71	10.871%	$79.5056	$79.51	$79.50	$79.50
Purchase #7	$198.73	4.690%	$208.0504	$208.05	$208.05	$208.10
7 purchase totals =	$677.01		$729.0541	$729.06	$729.10	$729.10