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	$247.51	7.251%	$265.457	$265.46	$265.45	$265.50
Purchase #2	$73.94	5.639%	$78.1095	$78.11	$78.10	$78.10
Purchase #3	$213.26	3.660%	$221.0653	$221.07	$221.05	$221.10
Purchase #4	$43.49	10.141%	$47.9003	$47.90	$47.90	$47.90
Purchase #5	$201.46	8.599%	$218.7835	$218.78	$218.80	$218.80
Purchase #6	$66.91	6.536%	$71.2832	$71.28	$71.30	$71.30
Purchase #7	$97.79	3.547%	$101.2586	$101.26	$101.25	$101.30
7 purchase totals =	$944.36		$1,003.8574	$1,003.86	$1,003.85	$1,004.00