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	$212.52	6.583%	$226.5102	$226.51	$226.50	$226.50
Purchase #2	$139.26	3.199%	$143.7149	$143.71	$143.70	$143.70
Purchase #3	$78.86	12.755%	$88.9186	$88.92	$88.90	$88.90
Purchase #4	$154.85	11.579%	$172.7801	$172.78	$172.80	$172.80
Purchase #5	$152.75	5.670%	$161.4109	$161.41	$161.40	$161.40
Purchase #6	$27.27	3.682%	$28.2741	$28.27	$28.25	$28.30
Purchase #7	$90.87	8.757%	$98.8275	$98.83	$98.85	$98.80
7 purchase totals =	$856.38		$920.4363	$920.43	$920.40	$920.40