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	$35.43	6.592%	$37.7655	$37.77	$37.75	$37.80
Purchase #2	$211.43	12.342%	$237.5247	$237.52	$237.50	$237.50
Purchase #3	$126.34	13.455%	$143.339	$143.34	$143.35	$143.30
Purchase #4	$193.59	3.787%	$200.9213	$200.92	$200.90	$200.90
Purchase #5	$160.34	3.380%	$165.7595	$165.76	$165.75	$165.80
Purchase #6	$92.86	9.418%	$101.6056	$101.61	$101.60	$101.60
Purchase #7	$108.35	8.417%	$117.4698	$117.47	$117.45	$117.50
7 purchase totals =	$928.34		$1,004.3854	$1,004.39	$1,004.30	$1,004.40