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	$104.63	4.612%	$109.4555	$109.46	$109.45	$109.50
Purchase #2	$147.65	11.537%	$164.6844	$164.68	$164.70	$164.70
Purchase #3	$92.93	12.389%	$104.4431	$104.44	$104.45	$104.40
Purchase #4	$66.89	6.795%	$71.4352	$71.44	$71.45	$71.40
Purchase #5	$47.40	4.842%	$49.6951	$49.70	$49.70	$49.70
Purchase #6	$62.86	13.403%	$71.2851	$71.29	$71.30	$71.30
Purchase #7	$70.96	9.711%	$77.8509	$77.85	$77.85	$77.90
7 purchase totals =	$593.32		$648.8493	$648.86	$648.90	$648.90