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	$29.49	6.606%	$31.4381	$31.44	$31.45	$31.40
Purchase #2	$10.55	11.240%	$11.7358	$11.74	$11.75	$11.70
Purchase #3	$9.92	3.584%	$10.2755	$10.28	$10.30	$10.30
Purchase #4	$33.50	11.564%	$37.3739	$37.37	$37.35	$37.40
Purchase #5	$35.52	5.521%	$37.4811	$37.48	$37.50	$37.50
Purchase #6	$175.49	7.630%	$188.8799	$188.88	$188.90	$188.90
Purchase #7	$242.79	11.589%	$270.9269	$270.93	$270.95	$270.90
7 purchase totals =	$537.26		$588.1112	$588.12	$588.20	$588.10