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	$40.33	4.674%	$42.215	$42.22	$42.20	$42.20
Purchase #2	$125.48	6.840%	$134.0628	$134.06	$134.05	$134.10
Purchase #3	$110.79	5.264%	$116.622	$116.62	$116.60	$116.60
Purchase #4	$176.31	11.298%	$196.2295	$196.23	$196.25	$196.20
Purchase #5	$42.64	11.328%	$47.4703	$47.47	$47.45	$47.50
Purchase #6	$109.40	12.761%	$123.3605	$123.36	$123.35	$123.40
Purchase #7	$60.48	13.414%	$68.5928	$68.59	$68.60	$68.60
7 purchase totals =	$665.43		$728.5529	$728.55	$728.50	$728.60