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	$132.81	10.249%	$146.4217	$146.42	$146.40	$146.40
Purchase #2	$110.96	11.588%	$123.818	$123.82	$123.80	$123.80
Purchase #3	$79.60	7.311%	$85.4196	$85.42	$85.40	$85.40
Purchase #4	$72.52	4.566%	$75.8313	$75.83	$75.85	$75.80
Purchase #5	$144.94	12.143%	$162.5401	$162.54	$162.55	$162.50
Purchase #6	$68.57	6.686%	$73.1546	$73.15	$73.15	$73.20
Purchase #7	$71.60	9.613%	$78.4829	$78.48	$78.50	$78.50
7 purchase totals =	$681.00		$745.6682	$745.66	$745.65	$745.60