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	$85.28	3.862%	$88.5735	$88.57	$88.55	$88.60
Purchase #2	$189.73	8.423%	$205.711	$205.71	$205.70	$205.70
Purchase #3	$69.78	12.657%	$78.6121	$78.61	$78.60	$78.60
Purchase #4	$11.72	3.175%	$12.0921	$12.09	$12.10	$12.10
Purchase #5	$55.65	9.543%	$60.9607	$60.96	$60.95	$61.00
Purchase #6	$39.90	9.252%	$43.5915	$43.59	$43.60	$43.60
Purchase #7	$129.43	10.391%	$142.8791	$142.88	$142.90	$142.90
7 purchase totals =	$581.49		$632.4200	$632.41	$632.40	$632.50