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	$91.50	9.266%	$99.9784	$99.98	$100.00	$100.00
Purchase #2	$226.83	5.238%	$238.7114	$238.71	$238.70	$238.70
Purchase #3	$156.67	5.577%	$165.4075	$165.41	$165.40	$165.40
Purchase #4	$119.99	10.166%	$132.1882	$132.19	$132.20	$132.20
Purchase #5	$147.82	8.558%	$160.4704	$160.47	$160.45	$160.50
Purchase #6	$21.68	12.762%	$24.4468	$24.45	$24.45	$24.40
Purchase #7	$167.54	8.519%	$181.8127	$181.81	$181.80	$181.80
7 purchase totals =	$932.03		$1,003.0154	$1,003.02	$1,003.00	$1,003.00