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	$122.27	12.503%	$137.5574	$137.56	$137.55	$137.60
Purchase #2	$35.45	7.866%	$38.2385	$38.24	$38.25	$38.20
Purchase #3	$212.39	10.775%	$235.275	$235.28	$235.30	$235.30
Purchase #4	$250.99	7.700%	$270.3162	$270.32	$270.30	$270.30
Purchase #5	$219.31	3.723%	$227.4749	$227.47	$227.45	$227.50
Purchase #6	$149.62	5.310%	$157.5648	$157.56	$157.55	$157.60
Purchase #7	$85.26	4.709%	$89.2749	$89.27	$89.25	$89.30
7 purchase totals =	$1,075.29		$1,155.7017	$1,155.70	$1,155.65	$1,155.80