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	$239.81	7.838%	$258.6063	$258.61	$258.60	$258.60
Purchase #2	$39.73	6.593%	$42.3494	$42.35	$42.35	$42.30
Purchase #3	$232.56	5.639%	$245.6741	$245.67	$245.65	$245.70
Purchase #4	$9.32	4.156%	$9.7073	$9.71	$9.70	$9.70
Purchase #5	$99.53	3.786%	$103.2982	$103.30	$103.30	$103.30
Purchase #6	$72.59	8.665%	$78.8799	$78.88	$78.90	$78.90
Purchase #7	$109.88	12.803%	$123.9479	$123.95	$123.95	$123.90
7 purchase totals =	$803.42		$862.4631	$862.47	$862.45	$862.40