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	$40.60	6.383%	$43.1915	$43.19	$43.20	$43.20
Purchase #2	$38.36	11.781%	$42.8792	$42.88	$42.90	$42.90
Purchase #3	$169.82	11.431%	$189.2321	$189.23	$189.25	$189.20
Purchase #4	$141.84	7.596%	$152.6142	$152.61	$152.60	$152.60
Purchase #5	$184.60	6.229%	$196.0987	$196.10	$196.10	$196.10
Purchase #6	$47.41	4.176%	$49.3898	$49.39	$49.40	$49.40
Purchase #7	$157.25	7.328%	$168.7733	$168.77	$168.75	$168.80
7 purchase totals =	$779.88		$842.1788	$842.17	$842.20	$842.20