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	$204.53	8.318%	$221.5428	$221.54	$221.55	$221.50
Purchase #2	$206.88	12.862%	$233.4889	$233.49	$233.50	$233.50
Purchase #3	$46.35	13.501%	$52.6077	$52.61	$52.60	$52.60
Purchase #4	$215.43	6.231%	$228.8534	$228.85	$228.85	$228.90
Purchase #5	$134.42	10.430%	$148.44	$148.44	$148.45	$148.40
Purchase #6	$89.49	7.296%	$96.0192	$96.02	$96.00	$96.00
Purchase #7	$133.50	7.775%	$143.8796	$143.88	$143.90	$143.90
7 purchase totals =	$1,030.60		$1,124.8316	$1,124.83	$1,124.85	$1,124.80