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	$246.70	10.112%	$271.6463	$271.65	$271.65	$271.60
Purchase #2	$109.85	12.475%	$123.5538	$123.55	$123.55	$123.60
Purchase #3	$43.73	4.161%	$45.5496	$45.55	$45.55	$45.50
Purchase #4	$132.61	6.155%	$140.7721	$140.77	$140.75	$140.80
Purchase #5	$44.47	3.821%	$46.1692	$46.17	$46.15	$46.20
Purchase #6	$212.31	9.193%	$231.8277	$231.83	$231.85	$231.80
Purchase #7	$22.98	10.408%	$25.3718	$25.37	$25.35	$25.40
7 purchase totals =	$812.65		$884.8905	$884.89	$884.85	$884.90