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	$230.53	12.164%	$258.5717	$258.57	$258.55	$258.60
Purchase #2	$36.33	5.184%	$38.2133	$38.21	$38.20	$38.20
Purchase #3	$218.96	9.673%	$240.14	$240.14	$240.15	$240.10
Purchase #4	$109.78	12.172%	$123.1424	$123.14	$123.15	$123.10
Purchase #5	$100.39	13.686%	$114.1294	$114.13	$114.15	$114.10
Purchase #6	$212.90	9.674%	$233.4959	$233.50	$233.50	$233.50
Purchase #7	$230.91	12.141%	$258.9448	$258.94	$258.95	$258.90
7 purchase totals =	$1,139.80		$1,266.6375	$1,266.63	$1,266.65	$1,266.50