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	$106.51	13.168%	$120.5352	$120.54	$120.55	$120.50
Purchase #2	$141.41	10.807%	$156.6922	$156.69	$156.70	$156.70
Purchase #3	$165.66	6.787%	$176.9033	$176.90	$176.90	$176.90
Purchase #4	$158.25	7.298%	$169.7991	$169.80	$169.80	$169.80
Purchase #5	$55.51	10.581%	$61.3835	$61.38	$61.40	$61.40
Purchase #6	$83.94	10.338%	$92.6177	$92.62	$92.60	$92.60
Purchase #7	$171.83	11.380%	$191.3843	$191.38	$191.40	$191.40
7 purchase totals =	$883.11		$969.3153	$969.31	$969.35	$969.30