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	$160.65	12.637%	$180.9513	$180.95	$180.95	$181.00
Purchase #2	$110.50	5.439%	$116.5101	$116.51	$116.50	$116.50
Purchase #3	$97.25	12.601%	$109.5045	$109.50	$109.50	$109.50
Purchase #4	$72.31	8.513%	$78.4658	$78.47	$78.45	$78.50
Purchase #5	$144.26	3.126%	$148.7696	$148.77	$148.75	$148.80
Purchase #6	$201.51	8.301%	$218.2373	$218.24	$218.25	$218.20
Purchase #7	$243.73	12.779%	$274.8763	$274.88	$274.90	$274.90
7 purchase totals =	$1,030.21		$1,127.3149	$1,127.32	$1,127.30	$1,127.40