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	$29.60	6.486%	$31.5199	$31.52	$31.50	$31.50
Purchase #2	$27.50	3.814%	$28.5489	$28.55	$28.55	$28.50
Purchase #3	$128.42	10.588%	$142.0171	$142.02	$142.00	$142.00
Purchase #4	$68.97	13.679%	$78.4044	$78.40	$78.40	$78.40
Purchase #5	$227.56	12.357%	$255.6796	$255.68	$255.70	$255.70
Purchase #6	$120.91	13.337%	$137.0358	$137.04	$137.05	$137.00
Purchase #7	$47.46	13.254%	$53.7503	$53.75	$53.75	$53.80
7 purchase totals =	$650.42		$726.9560	$726.96	$726.95	$726.90