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	$240.57	9.267%	$262.8636	$262.86	$262.85	$262.90
Purchase #2	$131.49	4.537%	$137.4557	$137.46	$137.45	$137.50
Purchase #3	$93.79	6.588%	$99.9689	$99.97	$99.95	$100.00
Purchase #4	$69.67	11.144%	$77.434	$77.43	$77.45	$77.40
Purchase #5	$42.30	11.197%	$47.0363	$47.04	$47.05	$47.00
Purchase #6	$174.97	12.143%	$196.2166	$196.22	$196.20	$196.20
Purchase #7	$76.95	6.711%	$82.1141	$82.11	$82.10	$82.10
7 purchase totals =	$829.74		$903.0892	$903.09	$903.05	$903.10