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	$77.71	7.126%	$83.2476	$83.25	$83.25	$83.20
Purchase #2	$128.90	8.709%	$140.1259	$140.13	$140.15	$140.10
Purchase #3	$25.67	8.658%	$27.8925	$27.89	$27.90	$27.90
Purchase #4	$92.42	7.459%	$99.3136	$99.31	$99.30	$99.30
Purchase #5	$99.86	5.775%	$105.6269	$105.63	$105.65	$105.60
Purchase #6	$143.85	9.814%	$157.9674	$157.97	$157.95	$158.00
Purchase #7	$131.83	7.348%	$141.5169	$141.52	$141.50	$141.50
7 purchase totals =	$700.24		$755.6908	$755.70	$755.70	$755.60