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	$187.50	12.310%	$210.5813	$210.58	$210.60	$210.60
Purchase #2	$103.34	8.266%	$111.8821	$111.88	$111.90	$111.90
Purchase #3	$51.79	6.536%	$55.175	$55.18	$55.20	$55.20
Purchase #4	$139.37	7.853%	$150.3147	$150.31	$150.30	$150.30
Purchase #5	$47.85	5.340%	$50.4052	$50.41	$50.40	$50.40
Purchase #6	$136.93	13.860%	$155.9085	$155.91	$155.90	$155.90
Purchase #7	$59.37	7.327%	$63.72	$63.72	$63.70	$63.70
7 purchase totals =	$726.15		$797.9868	$797.99	$798.00	$798.00