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	$173.26	9.174%	$189.1549	$189.15	$189.15	$189.20
Purchase #2	$46.43	7.454%	$49.8909	$49.89	$49.90	$49.90
Purchase #3	$245.64	5.254%	$258.5459	$258.55	$258.55	$258.50
Purchase #4	$164.28	6.453%	$174.881	$174.88	$174.90	$174.90
Purchase #5	$44.45	3.165%	$45.8568	$45.86	$45.85	$45.90
Purchase #6	$31.27	11.772%	$34.9511	$34.95	$34.95	$35.00
Purchase #7	$246.32	5.123%	$258.939	$258.94	$258.95	$258.90
7 purchase totals =	$951.65		$1,012.2196	$1,012.22	$1,012.25	$1,012.30