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	$73.96	13.591%	$84.0119	$84.01	$84.00	$84.00
Purchase #2	$218.57	9.298%	$238.8926	$238.89	$238.90	$238.90
Purchase #3	$45.68	3.380%	$47.224	$47.22	$47.20	$47.20
Purchase #4	$204.27	4.491%	$213.4438	$213.44	$213.45	$213.40
Purchase #5	$125.25	4.807%	$131.2708	$131.27	$131.25	$131.30
Purchase #6	$42.43	11.530%	$47.3222	$47.32	$47.30	$47.30
Purchase #7	$96.35	7.426%	$103.505	$103.51	$103.50	$103.50
7 purchase totals =	$806.51		$865.6703	$865.66	$865.60	$865.60