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	$12.48	6.647%	$13.3095	$13.31	$13.30	$13.30
Purchase #2	$74.61	12.703%	$84.0877	$84.09	$84.10	$84.10
Purchase #3	$136.87	9.617%	$150.0328	$150.03	$150.05	$150.00
Purchase #4	$61.73	11.633%	$68.9111	$68.91	$68.90	$68.90
Purchase #5	$103.71	7.809%	$111.8087	$111.81	$111.80	$111.80
Purchase #6	$32.56	3.147%	$33.5847	$33.58	$33.60	$33.60
Purchase #7	$188.31	4.268%	$196.3471	$196.35	$196.35	$196.30
7 purchase totals =	$610.27		$658.0816	$658.08	$658.10	$658.00