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	$52.88	12.692%	$59.5915	$59.59	$59.60	$59.60
Purchase #2	$234.71	3.770%	$243.5586	$243.56	$243.55	$243.60
Purchase #3	$223.75	8.292%	$242.3034	$242.30	$242.30	$242.30
Purchase #4	$37.66	5.208%	$39.6213	$39.62	$39.60	$39.60
Purchase #5	$240.70	12.425%	$270.607	$270.61	$270.60	$270.60
Purchase #6	$32.51	10.554%	$35.9411	$35.94	$35.95	$35.90
Purchase #7	$249.88	12.237%	$280.4578	$280.46	$280.45	$280.50
7 purchase totals =	$1,072.09		$1,172.0807	$1,172.08	$1,172.05	$1,172.10