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	$167.96	7.439%	$180.4545	$180.45	$180.45	$180.50
Purchase #2	$63.72	9.492%	$69.7683	$69.77	$69.75	$69.80
Purchase #3	$114.62	10.372%	$126.5084	$126.51	$126.50	$126.50
Purchase #4	$181.53	9.367%	$198.5339	$198.53	$198.55	$198.50
Purchase #5	$147.61	9.822%	$162.1083	$162.11	$162.10	$162.10
Purchase #6	$72.53	8.386%	$78.6124	$78.61	$78.60	$78.60
Purchase #7	$247.96	10.119%	$273.0511	$273.05	$273.05	$273.10
7 purchase totals =	$995.93		$1,089.0369	$1,089.03	$1,089.00	$1,089.10