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	$203.81	7.205%	$218.4945	$218.49	$218.50	$218.50
Purchase #2	$104.67	9.259%	$114.3614	$114.36	$114.35	$114.40
Purchase #3	$58.30	13.723%	$66.3005	$66.30	$66.30	$66.30
Purchase #4	$128.79	11.230%	$143.2531	$143.25	$143.25	$143.30
Purchase #5	$237.91	10.498%	$262.8858	$262.89	$262.90	$262.90
Purchase #6	$109.25	13.560%	$124.0643	$124.06	$124.05	$124.10
Purchase #7	$78.56	11.865%	$87.8811	$87.88	$87.90	$87.90
7 purchase totals =	$921.29		$1,017.2407	$1,017.23	$1,017.25	$1,017.40