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	$82.77	9.788%	$90.8715	$90.87	$90.85	$90.90
Purchase #2	$137.87	12.678%	$155.3492	$155.35	$155.35	$155.30
Purchase #3	$36.85	5.721%	$38.9582	$38.96	$38.95	$39.00
Purchase #4	$143.79	6.435%	$153.0429	$153.04	$153.05	$153.00
Purchase #5	$96.57	7.163%	$103.4873	$103.49	$103.50	$103.50
Purchase #6	$191.91	9.630%	$210.3909	$210.39	$210.40	$210.40
Purchase #7	$222.73	13.290%	$252.3308	$252.33	$252.35	$252.30
7 purchase totals =	$912.49		$1,004.4308	$1,004.43	$1,004.45	$1,004.40