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	$218.66	9.846%	$240.1893	$240.19	$240.20	$240.20
Purchase #2	$171.56	10.665%	$189.8569	$189.86	$189.85	$189.90
Purchase #3	$110.98	6.165%	$117.8219	$117.82	$117.80	$117.80
Purchase #4	$103.55	8.766%	$112.6272	$112.63	$112.65	$112.60
Purchase #5	$106.45	5.140%	$111.9215	$111.92	$111.90	$111.90
Purchase #6	$65.88	6.462%	$70.1372	$70.14	$70.15	$70.10
Purchase #7	$178.66	5.229%	$188.0021	$188.00	$188.00	$188.00
7 purchase totals =	$955.74		$1,030.5561	$1,030.56	$1,030.55	$1,030.50