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	$18.93	7.195%	$20.292	$20.29	$20.30	$20.30
Purchase #2	$231.96	4.115%	$241.5052	$241.51	$241.50	$241.50
Purchase #3	$103.63	8.669%	$112.6137	$112.61	$112.60	$112.60
Purchase #4	$164.83	13.354%	$186.8414	$186.84	$186.85	$186.80
Purchase #5	$147.34	11.803%	$164.7305	$164.73	$164.75	$164.70
Purchase #6	$181.66	5.461%	$191.5805	$191.58	$191.60	$191.60
Purchase #7	$210.56	13.279%	$238.5203	$238.52	$238.50	$238.50
7 purchase totals =	$1,058.91		$1,156.0836	$1,156.08	$1,156.10	$1,156.00