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	$29.45	8.301%	$31.8946	$31.89	$31.90	$31.90
Purchase #2	$219.27	9.845%	$240.8571	$240.86	$240.85	$240.90
Purchase #3	$134.56	4.418%	$140.5049	$140.50	$140.50	$140.50
Purchase #4	$135.48	6.210%	$143.8933	$143.89	$143.90	$143.90
Purchase #5	$15.28	13.244%	$17.3037	$17.30	$17.30	$17.30
Purchase #6	$180.73	5.193%	$190.1153	$190.12	$190.10	$190.10
Purchase #7	$245.90	7.297%	$263.8433	$263.84	$263.85	$263.80
7 purchase totals =	$960.67		$1,028.4122	$1,028.40	$1,028.40	$1,028.40