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	$126.97	12.729%	$143.132	$143.13	$143.15	$143.10
Purchase #2	$163.50	12.624%	$184.1402	$184.14	$184.15	$184.10
Purchase #3	$123.52	6.755%	$131.8638	$131.86	$131.85	$131.90
Purchase #4	$144.90	10.837%	$160.6028	$160.60	$160.60	$160.60
Purchase #5	$31.93	4.630%	$33.4084	$33.41	$33.40	$33.40
Purchase #6	$240.38	4.767%	$251.8389	$251.84	$251.85	$251.80
Purchase #7	$177.49	4.726%	$185.8782	$185.88	$185.90	$185.90
7 purchase totals =	$1,008.69		$1,090.8643	$1,090.86	$1,090.90	$1,090.80