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	$7.35	5.480%	$7.7528	$7.75	$7.75	$7.80
Purchase #2	$232.64	7.683%	$250.5137	$250.51	$250.50	$250.50
Purchase #3	$222.49	12.575%	$250.4681	$250.47	$250.45	$250.50
Purchase #4	$119.53	11.359%	$133.1074	$133.11	$133.10	$133.10
Purchase #5	$87.36	3.599%	$90.5041	$90.50	$90.50	$90.50
Purchase #6	$185.55	10.856%	$205.6933	$205.69	$205.70	$205.70
Purchase #7	$181.59	3.832%	$188.5485	$188.55	$188.55	$188.50
7 purchase totals =	$1,036.51		$1,126.5879	$1,126.58	$1,126.55	$1,126.60