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	$235.84	12.443%	$265.1856	$265.19	$265.20	$265.20
Purchase #2	$245.45	11.612%	$273.9517	$273.95	$273.95	$274.00
Purchase #3	$117.49	8.170%	$127.0889	$127.09	$127.10	$127.10
Purchase #4	$69.34	3.628%	$71.8557	$71.86	$71.85	$71.90
Purchase #5	$53.37	3.646%	$55.3159	$55.32	$55.30	$55.30
Purchase #6	$28.37	10.592%	$31.375	$31.38	$31.40	$31.40
Purchase #7	$7.95	7.714%	$8.5633	$8.56	$8.55	$8.60
7 purchase totals =	$757.81		$833.3361	$833.35	$833.35	$833.50