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	$242.40	13.455%	$275.0149	$275.01	$275.00	$275.00
Purchase #2	$98.70	13.205%	$111.7333	$111.73	$111.75	$111.70
Purchase #3	$133.30	6.784%	$142.3431	$142.34	$142.35	$142.30
Purchase #4	$173.44	5.447%	$182.8873	$182.89	$182.90	$182.90
Purchase #5	$87.38	12.232%	$98.0683	$98.07	$98.05	$98.10
Purchase #6	$144.65	3.656%	$149.9384	$149.94	$149.95	$149.90
Purchase #7	$74.76	10.144%	$82.3437	$82.34	$82.35	$82.30
7 purchase totals =	$954.63		$1,042.3290	$1,042.32	$1,042.35	$1,042.20