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	$75.94	6.297%	$80.7219	$80.72	$80.70	$80.70
Purchase #2	$114.35	5.810%	$120.9937	$120.99	$121.00	$121.00
Purchase #3	$113.26	10.669%	$125.3437	$125.34	$125.35	$125.30
Purchase #4	$78.34	5.308%	$82.4983	$82.50	$82.50	$82.50
Purchase #5	$103.81	12.857%	$117.1569	$117.16	$117.15	$117.20
Purchase #6	$175.81	11.818%	$196.5872	$196.59	$196.60	$196.60
Purchase #7	$142.89	9.263%	$156.1259	$156.13	$156.15	$156.10
7 purchase totals =	$804.40		$879.4276	$879.43	$879.45	$879.40