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	$233.56	11.139%	$259.5762	$259.58	$259.60	$259.60
Purchase #2	$181.25	13.712%	$206.103	$206.10	$206.10	$206.10
Purchase #3	$176.33	8.310%	$190.983	$190.98	$191.00	$191.00
Purchase #4	$77.60	7.568%	$83.4728	$83.47	$83.45	$83.50
Purchase #5	$190.40	13.697%	$216.4791	$216.48	$216.50	$216.50
Purchase #6	$119.85	12.530%	$134.8672	$134.87	$134.85	$134.90
Purchase #7	$91.74	6.189%	$97.4178	$97.42	$97.40	$97.40
7 purchase totals =	$1,070.73		$1,188.8991	$1,188.90	$1,188.90	$1,189.00