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	$250.52	9.444%	$274.1791	$274.18	$274.20	$274.20
Purchase #2	$81.64	3.240%	$84.2851	$84.29	$84.30	$84.30
Purchase #3	$86.29	12.728%	$97.273	$97.27	$97.25	$97.30
Purchase #4	$121.57	4.132%	$126.5933	$126.59	$126.60	$126.60
Purchase #5	$53.41	11.183%	$59.3828	$59.38	$59.40	$59.40
Purchase #6	$167.59	12.220%	$188.0695	$188.07	$188.05	$188.10
Purchase #7	$176.67	6.737%	$188.5723	$188.57	$188.55	$188.60
7 purchase totals =	$937.69		$1,018.3551	$1,018.35	$1,018.35	$1,018.50