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	$80.90	8.530%	$87.8008	$87.80	$87.80	$87.80
Purchase #2	$72.64	13.499%	$82.4457	$82.45	$82.45	$82.40
Purchase #3	$213.95	12.224%	$240.1032	$240.10	$240.10	$240.10
Purchase #4	$95.37	10.859%	$105.7262	$105.73	$105.75	$105.70
Purchase #5	$50.43	7.346%	$54.1346	$54.13	$54.15	$54.10
Purchase #6	$103.92	9.270%	$113.5534	$113.55	$113.55	$113.60
Purchase #7	$36.70	9.325%	$40.1223	$40.12	$40.10	$40.10
7 purchase totals =	$653.91		$723.8862	$723.88	$723.90	$723.80