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	$203.38	6.506%	$216.6119	$216.61	$216.60	$216.60
Purchase #2	$250.68	8.175%	$271.1731	$271.17	$271.15	$271.20
Purchase #3	$36.95	12.607%	$41.6083	$41.61	$41.60	$41.60
Purchase #4	$28.45	10.793%	$31.5206	$31.52	$31.50	$31.50
Purchase #5	$107.50	9.746%	$117.977	$117.98	$118.00	$118.00
Purchase #6	$187.51	6.737%	$200.1425	$200.14	$200.15	$200.10
Purchase #7	$109.96	8.614%	$119.432	$119.43	$119.45	$119.40
7 purchase totals =	$924.43		$998.4654	$998.46	$998.45	$998.40