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	$35.84	12.407%	$40.2867	$40.29	$40.30	$40.30
Purchase #2	$45.60	6.364%	$48.502	$48.50	$48.50	$48.50
Purchase #3	$47.59	10.339%	$52.5103	$52.51	$52.50	$52.50
Purchase #4	$152.26	11.529%	$169.8141	$169.81	$169.80	$169.80
Purchase #5	$53.77	3.204%	$55.4928	$55.49	$55.50	$55.50
Purchase #6	$72.32	8.581%	$78.5258	$78.53	$78.55	$78.50
Purchase #7	$250.55	3.409%	$259.0912	$259.09	$259.10	$259.10
7 purchase totals =	$657.93		$704.2229	$704.22	$704.25	$704.20