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	$45.90	9.306%	$50.1715	$50.17	$50.15	$50.20
Purchase #2	$97.69	11.587%	$109.0093	$109.01	$109.00	$109.00
Purchase #3	$73.96	6.329%	$78.6409	$78.64	$78.65	$78.60
Purchase #4	$145.56	8.122%	$157.3824	$157.38	$157.40	$157.40
Purchase #5	$15.82	10.517%	$17.4838	$17.48	$17.50	$17.50
Purchase #6	$102.73	13.398%	$116.4938	$116.49	$116.50	$116.50
Purchase #7	$73.91	3.705%	$76.6484	$76.65	$76.65	$76.60
7 purchase totals =	$555.57		$605.8301	$605.82	$605.85	$605.80