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	$54.84	9.332%	$59.9577	$59.96	$59.95	$60.00
Purchase #2	$120.75	5.464%	$127.3478	$127.35	$127.35	$127.30
Purchase #3	$97.54	8.620%	$105.9479	$105.95	$105.95	$105.90
Purchase #4	$148.50	4.283%	$154.8603	$154.86	$154.85	$154.90
Purchase #5	$118.27	5.324%	$124.5667	$124.57	$124.55	$124.60
Purchase #6	$220.86	8.120%	$238.7938	$238.79	$238.80	$238.80
Purchase #7	$96.82	7.800%	$104.372	$104.37	$104.35	$104.40
7 purchase totals =	$857.58		$915.8462	$915.85	$915.80	$915.90