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	$249.87	12.205%	$280.3666	$280.37	$280.35	$280.40
Purchase #2	$144.50	12.137%	$162.038	$162.04	$162.05	$162.00
Purchase #3	$148.73	12.216%	$166.8989	$166.90	$166.90	$166.90
Purchase #4	$99.47	4.119%	$103.5672	$103.57	$103.55	$103.60
Purchase #5	$248.71	13.831%	$283.1091	$283.11	$283.10	$283.10
Purchase #6	$220.37	11.236%	$245.1308	$245.13	$245.15	$245.10
Purchase #7	$72.32	13.276%	$81.9212	$81.92	$81.90	$81.90
7 purchase totals =	$1,183.97		$1,323.0318	$1,323.04	$1,323.00	$1,323.00