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	$183.43	9.543%	$200.9347	$200.93	$200.95	$200.90
Purchase #2	$127.78	12.279%	$143.4701	$143.47	$143.45	$143.50
Purchase #3	$36.27	9.155%	$39.5905	$39.59	$39.60	$39.60
Purchase #4	$162.26	12.380%	$182.3478	$182.35	$182.35	$182.30
Purchase #5	$242.46	6.480%	$258.1714	$258.17	$258.15	$258.20
Purchase #6	$31.47	13.337%	$35.6672	$35.67	$35.65	$35.70
Purchase #7	$118.83	10.854%	$131.7278	$131.73	$131.75	$131.70
7 purchase totals =	$902.50		$991.9095	$991.91	$991.90	$991.90