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	$6.70	4.479%	$7.0001	$7.00	$7.00	$7.00
Purchase #2	$245.61	3.141%	$253.3246	$253.32	$253.30	$253.30
Purchase #3	$246.73	6.248%	$262.1457	$262.15	$262.15	$262.10
Purchase #4	$37.95	3.505%	$39.2801	$39.28	$39.30	$39.30
Purchase #5	$186.93	10.528%	$206.61	$206.61	$206.60	$206.60
Purchase #6	$159.86	7.646%	$172.0829	$172.08	$172.10	$172.10
Purchase #7	$224.57	7.789%	$242.0618	$242.06	$242.05	$242.10
7 purchase totals =	$1,108.35		$1,182.5052	$1,182.50	$1,182.50	$1,182.50