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	$61.94	7.746%	$66.7379	$66.74	$66.75	$66.70
Purchase #2	$91.72	10.715%	$101.5478	$101.55	$101.55	$101.50
Purchase #3	$40.33	11.622%	$45.0172	$45.02	$45.00	$45.00
Purchase #4	$110.53	11.123%	$122.8243	$122.82	$122.80	$122.80
Purchase #5	$141.95	13.175%	$160.6519	$160.65	$160.65	$160.70
Purchase #6	$185.54	7.175%	$198.8525	$198.85	$198.85	$198.90
Purchase #7	$56.46	10.535%	$62.4081	$62.41	$62.40	$62.40
7 purchase totals =	$688.47		$758.0397	$758.04	$758.00	$758.00