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	$89.45	13.851%	$101.8397	$101.84	$101.85	$101.80
Purchase #2	$133.64	6.860%	$142.8077	$142.81	$142.80	$142.80
Purchase #3	$131.28	12.857%	$148.1587	$148.16	$148.15	$148.20
Purchase #4	$177.82	12.652%	$200.3178	$200.32	$200.30	$200.30
Purchase #5	$99.86	3.291%	$103.1464	$103.15	$103.15	$103.10
Purchase #6	$35.51	3.266%	$36.6698	$36.67	$36.65	$36.70
Purchase #7	$120.37	3.475%	$124.5529	$124.55	$124.55	$124.60
7 purchase totals =	$787.93		$857.4930	$857.50	$857.45	$857.50