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	$75.45	3.168%	$77.8403	$77.84	$77.85	$77.80
Purchase #2	$6.82	7.173%	$7.3092	$7.31	$7.30	$7.30
Purchase #3	$131.29	13.609%	$149.1573	$149.16	$149.15	$149.20
Purchase #4	$237.28	7.774%	$255.7261	$255.73	$255.75	$255.70
Purchase #5	$71.83	9.500%	$78.6539	$78.65	$78.65	$78.70
Purchase #6	$28.45	12.588%	$32.0313	$32.03	$32.05	$32.00
Purchase #7	$217.81	3.577%	$225.6011	$225.60	$225.60	$225.60
7 purchase totals =	$768.93		$826.3192	$826.32	$826.35	$826.30