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	$84.76	5.393%	$89.3311	$89.33	$89.35	$89.30
Purchase #2	$155.41	4.618%	$162.5868	$162.59	$162.60	$162.60
Purchase #3	$136.37	4.688%	$142.763	$142.76	$142.75	$142.80
Purchase #4	$110.56	5.367%	$116.4938	$116.49	$116.50	$116.50
Purchase #5	$36.31	5.175%	$38.189	$38.19	$38.20	$38.20
Purchase #6	$120.98	10.567%	$133.764	$133.76	$133.75	$133.80
Purchase #7	$155.76	3.623%	$161.4032	$161.40	$161.40	$161.40
7 purchase totals =	$800.15		$844.5309	$844.52	$844.55	$844.60