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	$5.77	3.515%	$5.9728	$5.97	$5.95	$6.00
Purchase #2	$219.88	9.177%	$240.0584	$240.06	$240.05	$240.10
Purchase #3	$99.69	11.816%	$111.4694	$111.47	$111.45	$111.50
Purchase #4	$202.35	10.104%	$222.7954	$222.80	$222.80	$222.80
Purchase #5	$199.79	13.383%	$226.5279	$226.53	$226.55	$226.50
Purchase #6	$90.61	8.312%	$98.1415	$98.14	$98.15	$98.10
Purchase #7	$170.89	12.639%	$192.4888	$192.49	$192.50	$192.50
7 purchase totals =	$988.98		$1,097.4542	$1,097.46	$1,097.45	$1,097.50