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	$38.81	9.784%	$42.6072	$42.61	$42.60	$42.60
Purchase #2	$35.83	12.303%	$40.2382	$40.24	$40.25	$40.20
Purchase #3	$189.41	3.459%	$195.9617	$195.96	$195.95	$196.00
Purchase #4	$47.72	12.205%	$53.5442	$53.54	$53.55	$53.50
Purchase #5	$162.83	11.847%	$182.1205	$182.12	$182.10	$182.10
Purchase #6	$179.62	6.230%	$190.8103	$190.81	$190.80	$190.80
Purchase #7	$185.80	6.207%	$197.3326	$197.33	$197.35	$197.30
7 purchase totals =	$840.02		$902.6147	$902.61	$902.60	$902.50