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	$74.55	10.706%	$82.5313	$82.53	$82.55	$82.50
Purchase #2	$125.87	13.161%	$142.4358	$142.44	$142.45	$142.40
Purchase #3	$207.89	13.293%	$235.5248	$235.52	$235.50	$235.50
Purchase #4	$35.72	8.864%	$38.8862	$38.89	$38.90	$38.90
Purchase #5	$63.54	7.229%	$68.1333	$68.13	$68.15	$68.10
Purchase #6	$7.71	8.222%	$8.3439	$8.34	$8.35	$8.30
Purchase #7	$150.77	13.664%	$171.3712	$171.37	$171.35	$171.40
7 purchase totals =	$666.05		$747.2265	$747.22	$747.25	$747.10