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	$134.69	3.571%	$139.4998	$139.50	$139.50	$139.50
Purchase #2	$49.33	13.556%	$56.0172	$56.02	$56.00	$56.00
Purchase #3	$217.88	11.310%	$242.5222	$242.52	$242.50	$242.50
Purchase #4	$186.49	5.171%	$196.1334	$196.13	$196.15	$196.10
Purchase #5	$21.96	11.116%	$24.4011	$24.40	$24.40	$24.40
Purchase #6	$139.46	3.863%	$144.8473	$144.85	$144.85	$144.80
Purchase #7	$184.81	7.828%	$199.2769	$199.28	$199.30	$199.30
7 purchase totals =	$934.62		$1,002.6979	$1,002.70	$1,002.70	$1,002.60