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	$60.90	5.186%	$64.0583	$64.06	$64.05	$64.10
Purchase #2	$34.28	8.794%	$37.2946	$37.29	$37.30	$37.30
Purchase #3	$225.31	13.340%	$255.3664	$255.37	$255.35	$255.40
Purchase #4	$36.25	4.547%	$37.8983	$37.90	$37.90	$37.90
Purchase #5	$230.28	5.807%	$243.6524	$243.65	$243.65	$243.70
Purchase #6	$119.99	9.257%	$131.0975	$131.10	$131.10	$131.10
Purchase #7	$201.28	12.721%	$226.8848	$226.88	$226.90	$226.90
7 purchase totals =	$908.29		$996.2523	$996.25	$996.25	$996.40