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	$125.95	8.315%	$136.4227	$136.42	$136.40	$136.40
Purchase #2	$241.91	11.306%	$269.2603	$269.26	$269.25	$269.30
Purchase #3	$226.44	12.641%	$255.0643	$255.06	$255.05	$255.10
Purchase #4	$6.77	11.377%	$7.5402	$7.54	$7.55	$7.50
Purchase #5	$153.31	9.423%	$167.7564	$167.76	$167.75	$167.80
Purchase #6	$74.93	5.154%	$78.7919	$78.79	$78.80	$78.80
Purchase #7	$38.54	7.343%	$41.37	$41.37	$41.35	$41.40
7 purchase totals =	$867.85		$956.2058	$956.20	$956.15	$956.30