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	$85.33	4.521%	$89.1878	$89.19	$89.20	$89.20
Purchase #2	$179.43	13.852%	$204.2846	$204.28	$204.30	$204.30
Purchase #3	$80.66	5.483%	$85.0826	$85.08	$85.10	$85.10
Purchase #4	$156.59	10.402%	$172.8785	$172.88	$172.90	$172.90
Purchase #5	$235.76	12.744%	$265.8053	$265.81	$265.80	$265.80
Purchase #6	$17.52	6.392%	$18.6399	$18.64	$18.65	$18.60
Purchase #7	$192.59	12.839%	$217.3166	$217.32	$217.30	$217.30
7 purchase totals =	$947.88		$1,053.1953	$1,053.20	$1,053.25	$1,053.20