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	$88.39	13.577%	$100.3907	$100.39	$100.40	$100.40
Purchase #2	$57.48	4.628%	$60.1402	$60.14	$60.15	$60.10
Purchase #3	$27.43	12.360%	$30.8203	$30.82	$30.80	$30.80
Purchase #4	$206.43	10.405%	$227.909	$227.91	$227.90	$227.90
Purchase #5	$37.75	7.617%	$40.6254	$40.63	$40.65	$40.60
Purchase #6	$24.69	11.485%	$27.5256	$27.53	$27.55	$27.50
Purchase #7	$128.28	10.219%	$141.3889	$141.39	$141.40	$141.40
7 purchase totals =	$570.45		$628.8001	$628.81	$628.85	$628.70