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	$170.95	7.588%	$183.9217	$183.92	$183.90	$183.90
Purchase #2	$99.78	3.754%	$103.5257	$103.53	$103.55	$103.50
Purchase #3	$84.28	7.359%	$90.4822	$90.48	$90.50	$90.50
Purchase #4	$16.73	12.204%	$18.7717	$18.77	$18.75	$18.80
Purchase #5	$249.91	6.654%	$266.539	$266.54	$266.55	$266.50
Purchase #6	$237.66	7.371%	$255.1779	$255.18	$255.20	$255.20
Purchase #7	$217.98	3.483%	$225.5722	$225.57	$225.55	$225.60
7 purchase totals =	$1,077.29		$1,143.9904	$1,143.99	$1,144.00	$1,144.00