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	$137.63	12.858%	$155.3265	$155.33	$155.35	$155.30
Purchase #2	$35.46	6.852%	$37.8897	$37.89	$37.90	$37.90
Purchase #3	$44.74	6.265%	$47.543	$47.54	$47.55	$47.50
Purchase #4	$155.39	6.363%	$165.2775	$165.28	$165.30	$165.30
Purchase #5	$71.90	6.658%	$76.6871	$76.69	$76.70	$76.70
Purchase #6	$107.72	6.375%	$114.5872	$114.59	$114.60	$114.60
Purchase #7	$213.28	13.182%	$241.3946	$241.39	$241.40	$241.40
7 purchase totals =	$766.12		$838.7056	$838.71	$838.80	$838.70