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	$178.93	5.267%	$188.3542	$188.35	$188.35	$188.40
Purchase #2	$172.97	8.386%	$187.4753	$187.48	$187.50	$187.50
Purchase #3	$35.95	12.380%	$40.4006	$40.40	$40.40	$40.40
Purchase #4	$37.92	10.709%	$41.9809	$41.98	$42.00	$42.00
Purchase #5	$240.81	8.145%	$260.424	$260.42	$260.40	$260.40
Purchase #6	$40.29	7.643%	$43.3694	$43.37	$43.35	$43.40
Purchase #7	$91.47	7.505%	$98.3348	$98.33	$98.35	$98.30
7 purchase totals =	$798.34		$860.3392	$860.33	$860.35	$860.40