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	$20.54	10.856%	$22.7698	$22.77	$22.75	$22.80
Purchase #2	$83.80	5.378%	$88.3068	$88.31	$88.30	$88.30
Purchase #3	$149.77	12.469%	$168.4448	$168.44	$168.45	$168.40
Purchase #4	$205.64	12.287%	$230.907	$230.91	$230.90	$230.90
Purchase #5	$55.42	11.705%	$61.9069	$61.91	$61.90	$61.90
Purchase #6	$6.57	11.768%	$7.3432	$7.34	$7.35	$7.30
Purchase #7	$53.30	12.240%	$59.8239	$59.82	$59.80	$59.80
7 purchase totals =	$575.04		$639.5024	$639.50	$639.45	$639.40