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	$142.65	9.768%	$156.5841	$156.58	$156.60	$156.60
Purchase #2	$91.48	10.230%	$100.8384	$100.84	$100.85	$100.80
Purchase #3	$243.97	4.186%	$254.1826	$254.18	$254.20	$254.20
Purchase #4	$41.29	6.254%	$43.8723	$43.87	$43.85	$43.90
Purchase #5	$95.81	3.308%	$98.9794	$98.98	$99.00	$99.00
Purchase #6	$79.40	12.561%	$89.3734	$89.37	$89.35	$89.40
Purchase #7	$234.50	5.617%	$247.6719	$247.67	$247.65	$247.70
7 purchase totals =	$929.10		$991.5021	$991.49	$991.50	$991.60