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	$188.72	7.662%	$203.1797	$203.18	$203.20	$203.20
Purchase #2	$148.31	12.691%	$167.132	$167.13	$167.15	$167.10
Purchase #3	$202.46	10.411%	$223.5381	$223.54	$223.55	$223.50
Purchase #4	$126.51	4.475%	$132.1713	$132.17	$132.15	$132.20
Purchase #5	$42.65	9.136%	$46.5465	$46.55	$46.55	$46.50
Purchase #6	$119.61	3.645%	$123.9698	$123.97	$123.95	$124.00
Purchase #7	$205.83	12.144%	$230.826	$230.83	$230.85	$230.80
7 purchase totals =	$1,034.09		$1,127.3634	$1,127.37	$1,127.40	$1,127.30