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	$158.31	3.277%	$163.4978	$163.50	$163.50	$163.50
Purchase #2	$141.78	7.288%	$152.1129	$152.11	$152.10	$152.10
Purchase #3	$78.32	5.386%	$82.5383	$82.54	$82.55	$82.50
Purchase #4	$135.31	12.846%	$152.6919	$152.69	$152.70	$152.70
Purchase #5	$80.70	11.139%	$89.6892	$89.69	$89.70	$89.70
Purchase #6	$25.27	10.622%	$27.9542	$27.95	$27.95	$28.00
Purchase #7	$153.72	11.324%	$171.1273	$171.13	$171.15	$171.10
7 purchase totals =	$773.41		$839.6116	$839.61	$839.65	$839.60