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	$98.85	6.843%	$105.6143	$105.61	$105.60	$105.60
Purchase #2	$144.25	3.610%	$149.4574	$149.46	$149.45	$149.50
Purchase #3	$162.68	3.741%	$168.7659	$168.77	$168.75	$168.80
Purchase #4	$214.81	6.175%	$228.0745	$228.07	$228.05	$228.10
Purchase #5	$69.78	11.601%	$77.8752	$77.88	$77.90	$77.90
Purchase #6	$71.54	6.726%	$76.3518	$76.35	$76.35	$76.40
Purchase #7	$103.63	7.661%	$111.5691	$111.57	$111.55	$111.60
7 purchase totals =	$865.54		$917.7082	$917.71	$917.65	$917.90