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	$50.40	11.342%	$56.1164	$56.12	$56.10	$56.10
Purchase #2	$131.80	11.126%	$146.4641	$146.46	$146.45	$146.50
Purchase #3	$240.98	9.240%	$263.2466	$263.25	$263.25	$263.20
Purchase #4	$63.50	6.226%	$67.4535	$67.45	$67.45	$67.50
Purchase #5	$27.88	8.530%	$30.2582	$30.26	$30.25	$30.30
Purchase #6	$216.44	5.557%	$228.4676	$228.47	$228.45	$228.50
Purchase #7	$159.56	5.636%	$168.5528	$168.55	$168.55	$168.60
7 purchase totals =	$890.56		$960.5592	$960.56	$960.50	$960.70