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	$230.51	11.137%	$256.1819	$256.18	$256.20	$256.20
Purchase #2	$245.63	11.660%	$274.2705	$274.27	$274.25	$274.30
Purchase #3	$203.80	6.322%	$216.6842	$216.68	$216.70	$216.70
Purchase #4	$111.94	7.781%	$120.6501	$120.65	$120.65	$120.70
Purchase #5	$192.91	3.326%	$199.3262	$199.33	$199.35	$199.30
Purchase #6	$85.92	4.642%	$89.9084	$89.91	$89.90	$89.90
Purchase #7	$80.47	10.601%	$89.0006	$89.00	$89.00	$89.00
7 purchase totals =	$1,151.18		$1,246.0219	$1,246.02	$1,246.05	$1,246.10