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	$186.94	11.708%	$208.8269	$208.83	$208.85	$208.80
Purchase #2	$249.75	6.440%	$265.8339	$265.83	$265.85	$265.80
Purchase #3	$127.53	11.462%	$142.1475	$142.15	$142.15	$142.10
Purchase #4	$90.35	10.192%	$99.5585	$99.56	$99.55	$99.60
Purchase #5	$195.75	11.850%	$218.9464	$218.95	$218.95	$218.90
Purchase #6	$8.67	10.253%	$9.5589	$9.56	$9.55	$9.60
Purchase #7	$45.65	6.310%	$48.5305	$48.53	$48.55	$48.50
7 purchase totals =	$904.64		$993.4026	$993.41	$993.45	$993.30