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	$181.59	10.293%	$200.2811	$200.28	$200.30	$200.30
Purchase #2	$185.87	7.724%	$200.2266	$200.23	$200.25	$200.20
Purchase #3	$103.74	12.547%	$116.7563	$116.76	$116.75	$116.80
Purchase #4	$49.67	12.546%	$55.9016	$55.90	$55.90	$55.90
Purchase #5	$26.72	6.863%	$28.5538	$28.55	$28.55	$28.60
Purchase #6	$218.67	5.402%	$230.4826	$230.48	$230.50	$230.50
Purchase #7	$38.30	4.796%	$40.1369	$40.14	$40.15	$40.10
7 purchase totals =	$804.56		$872.3389	$872.34	$872.40	$872.40