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	$117.59	11.564%	$131.1881	$131.19	$131.20	$131.20
Purchase #2	$19.67	6.672%	$20.9824	$20.98	$21.00	$21.00
Purchase #3	$158.58	6.162%	$168.3517	$168.35	$168.35	$168.40
Purchase #4	$165.60	12.592%	$186.4524	$186.45	$186.45	$186.50
Purchase #5	$75.83	12.116%	$85.0176	$85.02	$85.00	$85.00
Purchase #6	$197.75	6.148%	$209.9077	$209.91	$209.90	$209.90
Purchase #7	$61.30	10.692%	$67.8542	$67.85	$67.85	$67.90
7 purchase totals =	$796.32		$869.7541	$869.75	$869.75	$869.90