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	$229.55	3.850%	$238.3877	$238.39	$238.40	$238.40
Purchase #2	$238.28	13.521%	$270.4978	$270.50	$270.50	$270.50
Purchase #3	$105.62	10.425%	$116.6309	$116.63	$116.65	$116.60
Purchase #4	$128.95	12.686%	$145.3086	$145.31	$145.30	$145.30
Purchase #5	$172.71	5.689%	$182.5355	$182.54	$182.55	$182.50
Purchase #6	$110.30	9.256%	$120.5094	$120.51	$120.50	$120.50
Purchase #7	$164.36	9.273%	$179.6011	$179.60	$179.60	$179.60
7 purchase totals =	$1,149.77		$1,253.4710	$1,253.48	$1,253.50	$1,253.40