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	$137.78	3.602%	$142.7428	$142.74	$142.75	$142.70
Purchase #2	$246.42	4.110%	$256.5479	$256.55	$256.55	$256.50
Purchase #3	$130.64	12.115%	$146.467	$146.47	$146.45	$146.50
Purchase #4	$175.88	8.866%	$191.4735	$191.47	$191.45	$191.50
Purchase #5	$52.96	3.184%	$54.6462	$54.65	$54.65	$54.60
Purchase #6	$165.60	5.507%	$174.7196	$174.72	$174.70	$174.70
Purchase #7	$229.57	5.507%	$242.2124	$242.21	$242.20	$242.20
7 purchase totals =	$1,138.85		$1,208.8094	$1,208.81	$1,208.75	$1,208.70