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	$18.82	11.181%	$20.9243	$20.92	$20.90	$20.90
Purchase #2	$168.63	13.203%	$190.8942	$190.89	$190.90	$190.90
Purchase #3	$242.83	11.357%	$270.4082	$270.41	$270.40	$270.40
Purchase #4	$248.73	5.581%	$262.6116	$262.61	$262.60	$262.60
Purchase #5	$112.76	6.170%	$119.7173	$119.72	$119.70	$119.70
Purchase #6	$31.73	5.113%	$33.3524	$33.35	$33.35	$33.40
Purchase #7	$125.90	5.373%	$132.6646	$132.66	$132.65	$132.70
7 purchase totals =	$949.40		$1,030.5726	$1,030.56	$1,030.50	$1,030.60