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	$94.98	13.222%	$107.5383	$107.54	$107.55	$107.50
Purchase #2	$217.50	4.790%	$227.9183	$227.92	$227.90	$227.90
Purchase #3	$16.30	11.232%	$18.1308	$18.13	$18.15	$18.10
Purchase #4	$230.37	5.229%	$242.416	$242.42	$242.40	$242.40
Purchase #5	$43.46	3.815%	$45.118	$45.12	$45.10	$45.10
Purchase #6	$139.81	4.651%	$146.3126	$146.31	$146.30	$146.30
Purchase #7	$88.47	4.640%	$92.575	$92.58	$92.60	$92.60
7 purchase totals =	$830.89		$880.0090	$880.02	$880.00	$879.90