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	$11.81	3.266%	$12.1957	$12.20	$12.20	$12.20
Purchase #2	$154.35	8.561%	$167.5639	$167.56	$167.55	$167.60
Purchase #3	$88.82	13.559%	$100.8631	$100.86	$100.85	$100.90
Purchase #4	$181.72	4.216%	$189.3813	$189.38	$189.40	$189.40
Purchase #5	$172.29	3.683%	$178.6354	$178.64	$178.65	$178.60
Purchase #6	$11.63	11.439%	$12.9604	$12.96	$12.95	$13.00
Purchase #7	$112.28	11.262%	$124.925	$124.93	$124.95	$124.90
7 purchase totals =	$732.90		$786.5248	$786.53	$786.55	$786.60