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	$99.96	12.262%	$112.2171	$112.22	$112.20	$112.20
Purchase #2	$222.42	7.463%	$239.0192	$239.02	$239.00	$239.00
Purchase #3	$78.84	5.152%	$82.9018	$82.90	$82.90	$82.90
Purchase #4	$137.78	11.867%	$154.1304	$154.13	$154.15	$154.10
Purchase #5	$146.67	10.611%	$162.2332	$162.23	$162.25	$162.20
Purchase #6	$110.61	6.357%	$117.6415	$117.64	$117.65	$117.60
Purchase #7	$123.58	10.218%	$136.2074	$136.21	$136.20	$136.20
7 purchase totals =	$919.86		$1,004.3506	$1,004.35	$1,004.35	$1,004.20