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	$51.69	6.168%	$54.8782	$54.88	$54.90	$54.90
Purchase #2	$188.60	4.112%	$196.3552	$196.36	$196.35	$196.40
Purchase #3	$217.50	12.506%	$244.7006	$244.70	$244.70	$244.70
Purchase #4	$138.73	5.719%	$146.664	$146.66	$146.65	$146.70
Purchase #5	$208.88	10.202%	$230.1899	$230.19	$230.20	$230.20
Purchase #6	$101.94	10.411%	$112.553	$112.55	$112.55	$112.60
Purchase #7	$16.69	11.478%	$18.6057	$18.61	$18.60	$18.60
7 purchase totals =	$924.03		$1,003.9466	$1,003.95	$1,003.95	$1,004.10