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	$89.90	9.641%	$98.5673	$98.57	$98.55	$98.60
Purchase #2	$178.63	3.737%	$185.3054	$185.31	$185.30	$185.30
Purchase #3	$201.59	10.332%	$222.4183	$222.42	$222.40	$222.40
Purchase #4	$51.82	3.197%	$53.4767	$53.48	$53.50	$53.50
Purchase #5	$68.91	13.111%	$77.9448	$77.94	$77.95	$77.90
Purchase #6	$222.78	6.383%	$237	$237.00	$237.00	$237.00
Purchase #7	$219.67	6.123%	$233.1204	$233.12	$233.10	$233.10
7 purchase totals =	$1,033.30		$1,107.8329	$1,107.84	$1,107.80	$1,107.80