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	$111.93	11.316%	$124.596	$124.60	$124.60	$124.60
Purchase #2	$78.90	4.533%	$82.4765	$82.48	$82.50	$82.50
Purchase #3	$239.97	10.541%	$265.2652	$265.27	$265.25	$265.30
Purchase #4	$25.78	4.556%	$26.9545	$26.95	$26.95	$27.00
Purchase #5	$162.95	12.583%	$183.454	$183.45	$183.45	$183.50
Purchase #6	$80.47	6.230%	$85.4833	$85.48	$85.50	$85.50
Purchase #7	$36.41	11.779%	$40.6987	$40.70	$40.70	$40.70
7 purchase totals =	$736.41		$808.9282	$808.93	$808.95	$809.10