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	$225.99	5.665%	$238.7923	$238.79	$238.80	$238.80
Purchase #2	$108.78	13.297%	$123.2445	$123.24	$123.25	$123.20
Purchase #3	$174.51	12.532%	$196.3796	$196.38	$196.40	$196.40
Purchase #4	$126.59	3.360%	$130.8434	$130.84	$130.85	$130.80
Purchase #5	$73.91	6.660%	$78.8324	$78.83	$78.85	$78.80
Purchase #6	$28.42	12.217%	$31.8921	$31.89	$31.90	$31.90
Purchase #7	$147.25	5.481%	$155.3208	$155.32	$155.30	$155.30
7 purchase totals =	$885.45		$955.3051	$955.29	$955.35	$955.20