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	$109.64	6.160%	$116.3938	$116.39	$116.40	$116.40
Purchase #2	$150.53	5.355%	$158.5909	$158.59	$158.60	$158.60
Purchase #3	$39.57	4.409%	$41.3146	$41.31	$41.30	$41.30
Purchase #4	$5.63	7.278%	$6.0398	$6.04	$6.05	$6.00
Purchase #5	$71.83	8.419%	$77.8774	$77.88	$77.90	$77.90
Purchase #6	$55.35	8.190%	$59.8832	$59.88	$59.90	$59.90
Purchase #7	$176.67	5.287%	$186.0105	$186.01	$186.00	$186.00
7 purchase totals =	$609.22		$646.1102	$646.10	$646.15	$646.10