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	$160.67	3.810%	$166.7915	$166.79	$166.80	$166.80
Purchase #2	$117.37	5.585%	$123.9251	$123.93	$123.95	$123.90
Purchase #3	$85.46	9.335%	$93.4377	$93.44	$93.45	$93.40
Purchase #4	$49.88	12.597%	$56.1634	$56.16	$56.15	$56.20
Purchase #5	$126.82	12.637%	$142.8462	$142.85	$142.85	$142.80
Purchase #6	$211.84	5.592%	$223.6861	$223.69	$223.70	$223.70
Purchase #7	$99.71	6.258%	$105.9499	$105.95	$105.95	$105.90
7 purchase totals =	$851.75		$912.7999	$912.81	$912.85	$912.70