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	$156.62	6.136%	$166.2302	$166.23	$166.25	$166.20
Purchase #2	$55.79	3.250%	$57.6032	$57.60	$57.60	$57.60
Purchase #3	$189.54	3.667%	$196.4904	$196.49	$196.50	$196.50
Purchase #4	$226.57	13.583%	$257.345	$257.35	$257.35	$257.30
Purchase #5	$94.89	3.612%	$98.3174	$98.32	$98.30	$98.30
Purchase #6	$174.96	12.106%	$196.1407	$196.14	$196.15	$196.10
Purchase #7	$18.27	6.214%	$19.4053	$19.41	$19.40	$19.40
7 purchase totals =	$916.64		$991.5322	$991.54	$991.55	$991.40