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	$123.54	3.112%	$127.3846	$127.38	$127.40	$127.40
Purchase #2	$198.99	12.357%	$223.5792	$223.58	$223.60	$223.60
Purchase #3	$75.90	9.222%	$82.8995	$82.90	$82.90	$82.90
Purchase #4	$90.46	12.512%	$101.7784	$101.78	$101.80	$101.80
Purchase #5	$81.93	12.233%	$91.9525	$91.95	$91.95	$92.00
Purchase #6	$225.50	13.560%	$256.0778	$256.08	$256.10	$256.10
Purchase #7	$247.31	13.325%	$280.2641	$280.26	$280.25	$280.30
7 purchase totals =	$1,043.63		$1,163.9361	$1,163.93	$1,164.00	$1,164.10