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	$42.95	5.512%	$45.3174	$45.32	$45.30	$45.30
Purchase #2	$65.89	10.620%	$72.8875	$72.89	$72.90	$72.90
Purchase #3	$239.71	6.381%	$255.0059	$255.01	$255.00	$255.00
Purchase #4	$108.81	4.694%	$113.9175	$113.92	$113.90	$113.90
Purchase #5	$187.82	3.382%	$194.1721	$194.17	$194.15	$194.20
Purchase #6	$127.27	5.394%	$134.1349	$134.13	$134.15	$134.10
Purchase #7	$120.38	4.180%	$125.4119	$125.41	$125.40	$125.40
7 purchase totals =	$892.83		$940.8472	$940.85	$940.80	$940.80