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	$107.28	9.365%	$117.3268	$117.33	$117.35	$117.30
Purchase #2	$233.67	10.449%	$258.0862	$258.09	$258.10	$258.10
Purchase #3	$52.40	8.608%	$56.9106	$56.91	$56.90	$56.90
Purchase #4	$245.37	12.273%	$275.4843	$275.48	$275.50	$275.50
Purchase #5	$67.85	8.197%	$73.4117	$73.41	$73.40	$73.40
Purchase #6	$37.53	13.533%	$42.6089	$42.61	$42.60	$42.60
Purchase #7	$39.43	10.737%	$43.6636	$43.66	$43.65	$43.70
7 purchase totals =	$783.53		$867.4921	$867.49	$867.50	$867.50