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	$130.48	12.578%	$146.8918	$146.89	$146.90	$146.90
Purchase #2	$143.43	4.670%	$150.1282	$150.13	$150.15	$150.10
Purchase #3	$241.31	7.463%	$259.319	$259.32	$259.30	$259.30
Purchase #4	$57.60	6.732%	$61.4776	$61.48	$61.50	$61.50
Purchase #5	$160.77	12.823%	$181.3855	$181.39	$181.40	$181.40
Purchase #6	$121.45	12.749%	$136.9337	$136.93	$136.95	$136.90
Purchase #7	$28.83	6.385%	$30.6708	$30.67	$30.65	$30.70
7 purchase totals =	$883.87		$966.8066	$966.81	$966.85	$966.80