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	$26.40	12.835%	$29.7884	$29.79	$29.80	$29.80
Purchase #2	$87.90	7.292%	$94.3097	$94.31	$94.30	$94.30
Purchase #3	$248.95	7.804%	$268.3781	$268.38	$268.40	$268.40
Purchase #4	$219.67	13.435%	$249.1827	$249.18	$249.20	$249.20
Purchase #5	$92.81	6.532%	$98.8723	$98.87	$98.85	$98.90
Purchase #6	$100.81	10.696%	$111.5926	$111.59	$111.60	$111.60
Purchase #7	$141.80	4.736%	$148.5156	$148.52	$148.50	$148.50
7 purchase totals =	$918.34		$1,000.6394	$1,000.64	$1,000.65	$1,000.70