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	$27.99	10.752%	$30.9995	$31.00	$31.00	$31.00
Purchase #2	$19.47	10.765%	$21.5659	$21.57	$21.55	$21.60
Purchase #3	$247.38	7.652%	$266.3095	$266.31	$266.30	$266.30
Purchase #4	$147.68	12.482%	$166.1134	$166.11	$166.10	$166.10
Purchase #5	$39.32	10.834%	$43.5799	$43.58	$43.60	$43.60
Purchase #6	$55.94	6.270%	$59.4474	$59.45	$59.45	$59.40
Purchase #7	$87.38	3.600%	$90.5257	$90.53	$90.55	$90.50
7 purchase totals =	$625.16		$678.5413	$678.55	$678.55	$678.50