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	$185.64	3.715%	$192.5365	$192.54	$192.55	$192.50
Purchase #2	$187.85	6.604%	$200.2556	$200.26	$200.25	$200.30
Purchase #3	$200.80	13.535%	$227.9783	$227.98	$228.00	$228.00
Purchase #4	$76.57	11.704%	$85.5318	$85.53	$85.55	$85.50
Purchase #5	$166.80	9.269%	$182.2607	$182.26	$182.25	$182.30
Purchase #6	$10.80	10.123%	$11.8933	$11.89	$11.90	$11.90
Purchase #7	$59.58	13.320%	$67.5161	$67.52	$67.50	$67.50
7 purchase totals =	$888.04		$967.9723	$967.98	$968.00	$968.00