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	$187.91	13.505%	$213.2872	$213.29	$213.30	$213.30
Purchase #2	$38.72	12.616%	$43.6049	$43.60	$43.60	$43.60
Purchase #3	$180.33	13.384%	$204.4654	$204.47	$204.45	$204.50
Purchase #4	$241.53	13.578%	$274.3249	$274.32	$274.30	$274.30
Purchase #5	$61.79	5.693%	$65.3077	$65.31	$65.30	$65.30
Purchase #6	$57.44	12.255%	$64.4793	$64.48	$64.50	$64.50
Purchase #7	$104.55	8.145%	$113.0656	$113.07	$113.05	$113.10
7 purchase totals =	$872.27		$978.5350	$978.54	$978.50	$978.60