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	$50.88	9.121%	$55.5208	$55.52	$55.50	$55.50
Purchase #2	$154.91	10.611%	$171.3475	$171.35	$171.35	$171.30
Purchase #3	$67.91	3.384%	$70.2081	$70.21	$70.20	$70.20
Purchase #4	$48.88	12.127%	$54.8077	$54.81	$54.80	$54.80
Purchase #5	$100.44	11.762%	$112.2538	$112.25	$112.25	$112.30
Purchase #6	$245.36	3.857%	$254.8235	$254.82	$254.80	$254.80
Purchase #7	$205.68	9.690%	$225.6104	$225.61	$225.60	$225.60
7 purchase totals =	$874.06		$944.5718	$944.57	$944.50	$944.50