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	$78.43	6.601%	$83.6072	$83.61	$83.60	$83.60
Purchase #2	$98.93	4.220%	$103.1048	$103.10	$103.10	$103.10
Purchase #3	$240.90	8.560%	$261.521	$261.52	$261.50	$261.50
Purchase #4	$213.83	11.426%	$238.2622	$238.26	$238.25	$238.30
Purchase #5	$143.96	11.532%	$160.5615	$160.56	$160.55	$160.60
Purchase #6	$188.78	6.602%	$201.2433	$201.24	$201.25	$201.20
Purchase #7	$37.76	8.460%	$40.9545	$40.95	$40.95	$41.00
7 purchase totals =	$1,002.59		$1,089.2545	$1,089.24	$1,089.20	$1,089.30