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	$208.57	6.381%	$221.8789	$221.88	$221.90	$221.90
Purchase #2	$105.84	11.123%	$117.6126	$117.61	$117.60	$117.60
Purchase #3	$82.32	9.755%	$90.3503	$90.35	$90.35	$90.40
Purchase #4	$149.50	6.860%	$159.7557	$159.76	$159.75	$159.80
Purchase #5	$233.48	11.793%	$261.0143	$261.01	$261.00	$261.00
Purchase #6	$202.51	6.381%	$215.4322	$215.43	$215.45	$215.40
Purchase #7	$92.38	6.262%	$98.1648	$98.16	$98.15	$98.20
7 purchase totals =	$1,074.60		$1,164.2088	$1,164.20	$1,164.20	$1,164.30