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	$101.50	6.452%	$108.0488	$108.05	$108.05	$108.00
Purchase #2	$223.25	12.465%	$251.0781	$251.08	$251.10	$251.10
Purchase #3	$147.34	10.361%	$162.6059	$162.61	$162.60	$162.60
Purchase #4	$204.41	5.634%	$215.9265	$215.93	$215.95	$215.90
Purchase #5	$93.85	10.645%	$103.8403	$103.84	$103.85	$103.80
Purchase #6	$170.28	7.186%	$182.5163	$182.52	$182.50	$182.50
Purchase #7	$146.80	6.592%	$156.4771	$156.48	$156.50	$156.50
7 purchase totals =	$1,087.43		$1,180.4930	$1,180.51	$1,180.55	$1,180.40