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	$68.27	11.357%	$76.0234	$76.02	$76.00	$76.00
Purchase #2	$110.76	6.221%	$117.6504	$117.65	$117.65	$117.70
Purchase #3	$32.90	4.239%	$34.2946	$34.29	$34.30	$34.30
Purchase #4	$87.79	13.383%	$99.5389	$99.54	$99.55	$99.50
Purchase #5	$186.99	7.213%	$200.4776	$200.48	$200.50	$200.50
Purchase #6	$31.59	4.126%	$32.8934	$32.89	$32.90	$32.90
Purchase #7	$243.92	6.551%	$259.8992	$259.90	$259.90	$259.90
7 purchase totals =	$762.22		$820.7775	$820.77	$820.80	$820.80