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	$7.46	5.792%	$7.8921	$7.89	$7.90	$7.90
Purchase #2	$141.32	6.639%	$150.7022	$150.70	$150.70	$150.70
Purchase #3	$157.78	11.299%	$175.6076	$175.61	$175.60	$175.60
Purchase #4	$180.84	4.726%	$189.3865	$189.39	$189.40	$189.40
Purchase #5	$123.72	6.540%	$131.8113	$131.81	$131.80	$131.80
Purchase #6	$168.89	11.593%	$188.4694	$188.47	$188.45	$188.50
Purchase #7	$90.28	12.519%	$101.5822	$101.58	$101.60	$101.60
7 purchase totals =	$870.29		$945.4513	$945.45	$945.45	$945.50