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	$37.93	11.762%	$42.3913	$42.39	$42.40	$42.40
Purchase #2	$51.92	3.214%	$53.5887	$53.59	$53.60	$53.60
Purchase #3	$236.32	6.341%	$251.3051	$251.31	$251.30	$251.30
Purchase #4	$163.96	6.280%	$174.2567	$174.26	$174.25	$174.30
Purchase #5	$250.55	3.706%	$259.8354	$259.84	$259.85	$259.80
Purchase #6	$71.45	4.120%	$74.3937	$74.39	$74.40	$74.40
Purchase #7	$196.69	11.136%	$218.5934	$218.59	$218.60	$218.60
7 purchase totals =	$1,008.82		$1,074.3643	$1,074.37	$1,074.40	$1,074.40