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	$53.68	11.580%	$59.8961	$59.90	$59.90	$59.90
Purchase #2	$110.32	3.665%	$114.3632	$114.36	$114.35	$114.40
Purchase #3	$34.83	10.537%	$38.5	$38.50	$38.50	$38.50
Purchase #4	$203.51	9.317%	$222.471	$222.47	$222.45	$222.50
Purchase #5	$172.79	7.860%	$186.3713	$186.37	$186.35	$186.40
Purchase #6	$179.37	4.560%	$187.5493	$187.55	$187.55	$187.50
Purchase #7	$171.52	3.263%	$177.1167	$177.12	$177.10	$177.10
7 purchase totals =	$926.02		$986.2676	$986.27	$986.20	$986.30