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	$85.39	3.421%	$88.3112	$88.31	$88.30	$88.30
Purchase #2	$219.89	8.671%	$238.9567	$238.96	$238.95	$239.00
Purchase #3	$65.59	11.607%	$73.203	$73.20	$73.20	$73.20
Purchase #4	$26.46	7.296%	$28.3905	$28.39	$28.40	$28.40
Purchase #5	$78.56	11.340%	$87.4687	$87.47	$87.45	$87.50
Purchase #6	$220.64	13.796%	$251.0795	$251.08	$251.10	$251.10
Purchase #7	$108.45	13.850%	$123.4703	$123.47	$123.45	$123.50
7 purchase totals =	$804.98		$890.8799	$890.88	$890.85	$891.00