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	$122.30	8.539%	$132.7432	$132.74	$132.75	$132.70
Purchase #2	$178.66	6.445%	$190.1746	$190.17	$190.15	$190.20
Purchase #3	$184.59	6.244%	$196.1158	$196.12	$196.10	$196.10
Purchase #4	$168.65	10.569%	$186.4746	$186.47	$186.45	$186.50
Purchase #5	$27.54	3.615%	$28.5356	$28.54	$28.55	$28.50
Purchase #6	$112.80	5.780%	$119.3198	$119.32	$119.30	$119.30
Purchase #7	$15.91	7.467%	$17.098	$17.10	$17.10	$17.10
7 purchase totals =	$810.45		$870.4616	$870.46	$870.40	$870.40