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	$58.87	9.721%	$64.5928	$64.59	$64.60	$64.60
Purchase #2	$177.46	12.753%	$200.0915	$200.09	$200.10	$200.10
Purchase #3	$141.92	12.199%	$159.2328	$159.23	$159.25	$159.20
Purchase #4	$166.34	10.827%	$184.3496	$184.35	$184.35	$184.30
Purchase #5	$183.90	6.631%	$196.0944	$196.09	$196.10	$196.10
Purchase #6	$144.51	13.641%	$164.2226	$164.22	$164.20	$164.20
Purchase #7	$13.85	9.755%	$15.2011	$15.20	$15.20	$15.20
7 purchase totals =	$886.85		$983.7848	$983.77	$983.80	$983.70