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	$54.36	11.871%	$60.8131	$60.81	$60.80	$60.80
Purchase #2	$45.95	13.426%	$52.1192	$52.12	$52.10	$52.10
Purchase #3	$247.65	13.412%	$280.8648	$280.86	$280.85	$280.90
Purchase #4	$182.87	3.599%	$189.4515	$189.45	$189.45	$189.50
Purchase #5	$48.78	9.293%	$53.3131	$53.31	$53.30	$53.30
Purchase #6	$35.82	11.341%	$39.8823	$39.88	$39.90	$39.90
Purchase #7	$89.46	10.420%	$98.7817	$98.78	$98.80	$98.80
7 purchase totals =	$704.89		$775.2257	$775.21	$775.20	$775.30