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	$11.82	13.569%	$13.4239	$13.42	$13.40	$13.40
Purchase #2	$151.46	11.255%	$168.5068	$168.51	$168.50	$168.50
Purchase #3	$31.26	6.328%	$33.2381	$33.24	$33.25	$33.20
Purchase #4	$222.46	7.706%	$239.6028	$239.60	$239.60	$239.60
Purchase #5	$240.26	12.306%	$269.8264	$269.83	$269.85	$269.80
Purchase #6	$40.32	9.226%	$44.0399	$44.04	$44.05	$44.00
Purchase #7	$246.55	11.112%	$273.9466	$273.95	$273.95	$273.90
7 purchase totals =	$944.13		$1,042.5845	$1,042.59	$1,042.60	$1,042.40