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	$156.36	8.801%	$170.1212	$170.12	$170.10	$170.10
Purchase #2	$18.61	5.430%	$19.6205	$19.62	$19.60	$19.60
Purchase #3	$94.48	13.590%	$107.3198	$107.32	$107.30	$107.30
Purchase #4	$107.53	5.517%	$113.4624	$113.46	$113.45	$113.50
Purchase #5	$72.99	12.838%	$82.3605	$82.36	$82.35	$82.40
Purchase #6	$97.59	7.468%	$104.878	$104.88	$104.90	$104.90
Purchase #7	$172.34	11.493%	$192.147	$192.15	$192.15	$192.10
7 purchase totals =	$719.90		$789.9094	$789.91	$789.85	$789.90