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	$103.42	5.708%	$109.3232	$109.32	$109.30	$109.30
Purchase #2	$106.34	3.328%	$109.879	$109.88	$109.90	$109.90
Purchase #3	$157.93	8.426%	$171.2372	$171.24	$171.25	$171.20
Purchase #4	$33.33	6.155%	$35.3815	$35.38	$35.40	$35.40
Purchase #5	$9.76	6.846%	$10.4282	$10.43	$10.45	$10.40
Purchase #6	$7.50	12.235%	$8.4176	$8.42	$8.40	$8.40
Purchase #7	$179.92	13.208%	$203.6838	$203.68	$203.70	$203.70
7 purchase totals =	$598.20		$648.3505	$648.35	$648.40	$648.30