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	$28.88	13.332%	$32.7303	$32.73	$32.75	$32.70
Purchase #2	$38.59	4.806%	$40.4446	$40.44	$40.45	$40.40
Purchase #3	$206.69	9.587%	$226.5054	$226.51	$226.50	$226.50
Purchase #4	$183.75	11.417%	$204.7287	$204.73	$204.75	$204.70
Purchase #5	$82.58	13.562%	$93.7795	$93.78	$93.80	$93.80
Purchase #6	$78.61	11.839%	$87.9166	$87.92	$87.90	$87.90
Purchase #7	$81.30	10.595%	$89.9137	$89.91	$89.90	$89.90
7 purchase totals =	$700.40		$776.0188	$776.02	$776.05	$775.90