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	$63.79	4.587%	$66.716	$66.72	$66.70	$66.70
Purchase #2	$130.59	11.504%	$145.6131	$145.61	$145.60	$145.60
Purchase #3	$197.68	11.486%	$220.3855	$220.39	$220.40	$220.40
Purchase #4	$86.70	4.449%	$90.5573	$90.56	$90.55	$90.60
Purchase #5	$89.41	13.740%	$101.6949	$101.69	$101.70	$101.70
Purchase #6	$81.70	6.211%	$86.7744	$86.77	$86.75	$86.80
Purchase #7	$63.39	5.259%	$66.7237	$66.72	$66.70	$66.70
7 purchase totals =	$713.26		$778.4649	$778.46	$778.40	$778.50