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	$228.83	13.690%	$260.1568	$260.16	$260.15	$260.20
Purchase #2	$28.56	13.400%	$32.387	$32.39	$32.40	$32.40
Purchase #3	$104.70	3.860%	$108.7414	$108.74	$108.75	$108.70
Purchase #4	$89.28	8.558%	$96.9206	$96.92	$96.90	$96.90
Purchase #5	$106.83	5.561%	$112.7708	$112.77	$112.75	$112.80
Purchase #6	$28.82	10.719%	$31.9092	$31.91	$31.90	$31.90
Purchase #7	$27.59	7.510%	$29.662	$29.66	$29.65	$29.70
7 purchase totals =	$614.61		$672.5478	$672.55	$672.50	$672.60