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	$114.41	8.373%	$123.9895	$123.99	$124.00	$124.00
Purchase #2	$239.83	12.710%	$270.3124	$270.31	$270.30	$270.30
Purchase #3	$38.58	5.842%	$40.8338	$40.83	$40.85	$40.80
Purchase #4	$62.97	6.262%	$66.9132	$66.91	$66.90	$66.90
Purchase #5	$47.33	13.735%	$53.8308	$53.83	$53.85	$53.80
Purchase #6	$38.57	11.367%	$42.9543	$42.95	$42.95	$43.00
Purchase #7	$53.70	4.688%	$56.2175	$56.22	$56.20	$56.20
7 purchase totals =	$595.39		$655.0515	$655.04	$655.05	$655.00