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	$71.39	13.459%	$80.9984	$81.00	$81.00	$81.00
Purchase #2	$71.56	12.666%	$80.6238	$80.62	$80.60	$80.60
Purchase #3	$218.84	5.745%	$231.4124	$231.41	$231.40	$231.40
Purchase #4	$78.55	10.850%	$87.0727	$87.07	$87.05	$87.10
Purchase #5	$51.55	3.737%	$53.4764	$53.48	$53.50	$53.50
Purchase #6	$101.77	7.653%	$109.5585	$109.56	$109.55	$109.60
Purchase #7	$11.30	4.581%	$11.8177	$11.82	$11.80	$11.80
7 purchase totals =	$604.96		$654.9599	$654.96	$654.90	$655.00