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	$242.62	13.366%	$275.0486	$275.05	$275.05	$275.00
Purchase #2	$202.36	12.410%	$227.4729	$227.47	$227.45	$227.50
Purchase #3	$62.50	7.131%	$66.9569	$66.96	$66.95	$67.00
Purchase #4	$57.45	6.648%	$61.2693	$61.27	$61.25	$61.30
Purchase #5	$123.89	10.473%	$136.865	$136.87	$136.85	$136.90
Purchase #6	$139.67	11.223%	$155.3452	$155.35	$155.35	$155.30
Purchase #7	$155.35	11.564%	$173.3147	$173.31	$173.30	$173.30
7 purchase totals =	$983.84		$1,096.2726	$1,096.28	$1,096.20	$1,096.30