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	$131.81	4.215%	$137.3658	$137.37	$137.35	$137.40
Purchase #2	$116.54	9.202%	$127.264	$127.26	$127.25	$127.30
Purchase #3	$179.28	12.801%	$202.2296	$202.23	$202.25	$202.20
Purchase #4	$84.81	5.364%	$89.3592	$89.36	$89.35	$89.40
Purchase #5	$152.81	5.362%	$161.0037	$161.00	$161.00	$161.00
Purchase #6	$152.46	10.236%	$168.0658	$168.07	$168.05	$168.10
Purchase #7	$95.80	10.586%	$105.9414	$105.94	$105.95	$105.90
7 purchase totals =	$913.51		$991.2295	$991.23	$991.20	$991.30