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	$90.52	11.488%	$100.9189	$100.92	$100.90	$100.90
Purchase #2	$25.42	8.633%	$27.6145	$27.61	$27.60	$27.60
Purchase #3	$180.77	6.539%	$192.5906	$192.59	$192.60	$192.60
Purchase #4	$59.99	5.872%	$63.5126	$63.51	$63.50	$63.50
Purchase #5	$79.68	8.454%	$86.4161	$86.42	$86.40	$86.40
Purchase #6	$214.54	11.610%	$239.4481	$239.45	$239.45	$239.40
Purchase #7	$207.85	10.394%	$229.4539	$229.45	$229.45	$229.50
7 purchase totals =	$858.77		$939.9547	$939.95	$939.90	$939.90