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	$43.93	11.605%	$49.0281	$49.03	$49.05	$49.00
Purchase #2	$107.56	11.409%	$119.8315	$119.83	$119.85	$119.80
Purchase #3	$169.91	11.541%	$189.5193	$189.52	$189.50	$189.50
Purchase #4	$95.30	9.306%	$104.1686	$104.17	$104.15	$104.20
Purchase #5	$90.52	3.472%	$93.6629	$93.66	$93.65	$93.70
Purchase #6	$19.72	6.293%	$20.961	$20.96	$20.95	$21.00
Purchase #7	$71.58	9.466%	$78.3558	$78.36	$78.35	$78.40
7 purchase totals =	$598.52		$655.5272	$655.53	$655.50	$655.60