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	$244.63	5.298%	$257.5905	$257.59	$257.60	$257.60
Purchase #2	$12.77	7.747%	$13.7593	$13.76	$13.75	$13.80
Purchase #3	$105.45	10.330%	$116.343	$116.34	$116.35	$116.30
Purchase #4	$112.89	13.289%	$127.892	$127.89	$127.90	$127.90
Purchase #5	$59.29	10.254%	$65.3696	$65.37	$65.35	$65.40
Purchase #6	$82.27	7.501%	$88.4411	$88.44	$88.45	$88.40
Purchase #7	$155.75	9.109%	$169.9373	$169.94	$169.95	$169.90
7 purchase totals =	$773.05		$839.3328	$839.33	$839.35	$839.30