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	$111.70	10.596%	$123.5357	$123.54	$123.55	$123.50
Purchase #2	$104.83	8.180%	$113.4051	$113.41	$113.40	$113.40
Purchase #3	$132.89	11.406%	$148.0474	$148.05	$148.05	$148.00
Purchase #4	$166.30	11.686%	$185.7338	$185.73	$185.75	$185.70
Purchase #5	$150.27	11.252%	$167.1784	$167.18	$167.20	$167.20
Purchase #6	$47.43	7.661%	$51.0636	$51.06	$51.05	$51.10
Purchase #7	$170.60	13.339%	$193.3563	$193.36	$193.35	$193.40
7 purchase totals =	$884.02		$982.3203	$982.33	$982.35	$982.30