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	$67.96	6.406%	$72.3135	$72.31	$72.30	$72.30
Purchase #2	$95.83	8.139%	$103.6296	$103.63	$103.65	$103.60
Purchase #3	$94.36	5.200%	$99.2667	$99.27	$99.25	$99.30
Purchase #4	$83.80	6.193%	$88.9897	$88.99	$89.00	$89.00
Purchase #5	$244.44	6.443%	$260.1893	$260.19	$260.20	$260.20
Purchase #6	$145.54	4.846%	$152.5929	$152.59	$152.60	$152.60
Purchase #7	$22.25	13.590%	$25.2738	$25.27	$25.25	$25.30
7 purchase totals =	$754.18		$802.2555	$802.25	$802.25	$802.30