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	$66.34	13.805%	$75.4982	$75.50	$75.50	$75.50
Purchase #2	$84.47	7.124%	$90.4876	$90.49	$90.50	$90.50
Purchase #3	$141.83	13.457%	$160.9161	$160.92	$160.90	$160.90
Purchase #4	$81.64	5.850%	$86.4159	$86.42	$86.40	$86.40
Purchase #5	$63.30	4.302%	$66.0232	$66.02	$66.00	$66.00
Purchase #6	$156.42	3.739%	$162.2685	$162.27	$162.25	$162.30
Purchase #7	$30.32	11.234%	$33.7261	$33.73	$33.75	$33.70
7 purchase totals =	$624.32		$675.3356	$675.35	$675.30	$675.30