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	$96.31	3.719%	$99.8918	$99.89	$99.90	$99.90
Purchase #2	$142.99	9.177%	$156.1122	$156.11	$156.10	$156.10
Purchase #3	$226.53	5.711%	$239.4671	$239.47	$239.45	$239.50
Purchase #4	$30.67	3.312%	$31.6858	$31.69	$31.70	$31.70
Purchase #5	$167.80	7.325%	$180.0914	$180.09	$180.10	$180.10
Purchase #6	$176.53	7.444%	$189.6709	$189.67	$189.65	$189.70
Purchase #7	$89.89	10.632%	$99.4471	$99.45	$99.45	$99.40
7 purchase totals =	$930.72		$996.3663	$996.37	$996.35	$996.40