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	$245.79	10.413%	$271.3841	$271.38	$271.40	$271.40
Purchase #2	$132.56	12.510%	$149.1433	$149.14	$149.15	$149.10
Purchase #3	$32.33	11.159%	$35.9377	$35.94	$35.95	$35.90
Purchase #4	$225.27	9.419%	$246.4882	$246.49	$246.50	$246.50
Purchase #5	$40.84	4.262%	$42.5806	$42.58	$42.60	$42.60
Purchase #6	$39.50	10.128%	$43.5006	$43.50	$43.50	$43.50
Purchase #7	$104.56	7.703%	$112.6143	$112.61	$112.60	$112.60
7 purchase totals =	$820.85		$901.6488	$901.64	$901.70	$901.60