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	$91.47	12.121%	$102.5571	$102.56	$102.55	$102.60
Purchase #2	$150.86	6.143%	$160.1273	$160.13	$160.15	$160.10
Purchase #3	$193.48	12.665%	$217.9842	$217.98	$218.00	$218.00
Purchase #4	$155.37	6.415%	$165.337	$165.34	$165.35	$165.30
Purchase #5	$186.82	13.583%	$212.1958	$212.20	$212.20	$212.20
Purchase #6	$111.34	4.570%	$116.4282	$116.43	$116.45	$116.40
Purchase #7	$144.97	13.393%	$164.3858	$164.39	$164.40	$164.40
7 purchase totals =	$1,034.31		$1,139.0154	$1,139.03	$1,139.10	$1,139.00