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	$123.81	13.266%	$140.2346	$140.23	$140.25	$140.20
Purchase #2	$129.54	11.539%	$144.4876	$144.49	$144.50	$144.50
Purchase #3	$124.39	3.568%	$128.8282	$128.83	$128.85	$128.80
Purchase #4	$137.28	3.595%	$142.2152	$142.22	$142.20	$142.20
Purchase #5	$107.88	3.779%	$111.9568	$111.96	$111.95	$112.00
Purchase #6	$114.86	3.256%	$118.5998	$118.60	$118.60	$118.60
Purchase #7	$200.94	3.282%	$207.5349	$207.53	$207.55	$207.50
7 purchase totals =	$938.70		$993.8571	$993.86	$993.90	$993.80