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	$215.38	6.703%	$229.8169	$229.82	$229.80	$229.80
Purchase #2	$30.94	7.758%	$33.3403	$33.34	$33.35	$33.30
Purchase #3	$110.34	12.253%	$123.86	$123.86	$123.85	$123.90
Purchase #4	$88.69	10.152%	$97.6938	$97.69	$97.70	$97.70
Purchase #5	$52.95	11.321%	$58.9445	$58.94	$58.95	$58.90
Purchase #6	$62.72	12.483%	$70.5493	$70.55	$70.55	$70.50
Purchase #7	$51.43	7.300%	$55.1844	$55.18	$55.20	$55.20
7 purchase totals =	$612.45		$669.3892	$669.38	$669.40	$669.30