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	$227.94	11.138%	$253.328	$253.33	$253.35	$253.30
Purchase #2	$54.46	9.424%	$59.5923	$59.59	$59.60	$59.60
Purchase #3	$95.59	7.228%	$102.4992	$102.50	$102.50	$102.50
Purchase #4	$154.96	8.641%	$168.3501	$168.35	$168.35	$168.40
Purchase #5	$97.40	4.603%	$101.8833	$101.88	$101.90	$101.90
Purchase #6	$127.79	12.133%	$143.2948	$143.29	$143.30	$143.30
Purchase #7	$63.31	12.713%	$71.3586	$71.36	$71.35	$71.40
7 purchase totals =	$821.45		$900.3063	$900.30	$900.35	$900.40