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	$126.48	7.538%	$136.0141	$136.01	$136.00	$136.00
Purchase #2	$52.25	8.864%	$56.8814	$56.88	$56.90	$56.90
Purchase #3	$106.86	11.557%	$119.2098	$119.21	$119.20	$119.20
Purchase #4	$62.63	13.205%	$70.9003	$70.90	$70.90	$70.90
Purchase #5	$120.27	11.331%	$133.8978	$133.90	$133.90	$133.90
Purchase #6	$143.73	7.855%	$155.02	$155.02	$155.00	$155.00
Purchase #7	$34.86	7.799%	$37.5787	$37.58	$37.60	$37.60
7 purchase totals =	$647.08		$709.5021	$709.50	$709.50	$709.50