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	$55.79	6.557%	$59.4482	$59.45	$59.45	$59.40
Purchase #2	$132.90	5.787%	$140.5909	$140.59	$140.60	$140.60
Purchase #3	$35.45	10.559%	$39.1932	$39.19	$39.20	$39.20
Purchase #4	$158.81	6.262%	$168.7547	$168.75	$168.75	$168.80
Purchase #5	$37.39	8.279%	$40.4855	$40.49	$40.50	$40.50
Purchase #6	$123.78	12.457%	$139.1993	$139.20	$139.20	$139.20
Purchase #7	$69.33	5.811%	$73.3588	$73.36	$73.35	$73.40
7 purchase totals =	$613.45		$661.0306	$661.03	$661.05	$661.10